Some people would say that it is, but there are a number of things that make me find this belief a bit unlikely. I generally support right of contract, which I think gets lost a lot in this discussion due to the existence of exploitative contracts, but I don't think exceptions disprove the rule. I'm willing to concede contracts as theft in the cases of deception or force, but other than that I'll defend right of contract.
Child labor falls under deception if the kids are too young to grasp the implications of the contract. So does taking advantage of insane people or paying someone to cut their arm off, since anyone who agrees to that is probably insane. Force includes blackmail or threatening to violate other rights/harm people if they don't sign the contract. Refusing to give someone something you owe them or access to a common resource unless they sign a contract is a rights violation, but the rights violation is failure to pay a debt or stealing a common resource, which is separate from the contract itself. I think some people would argue employment is deceptive since the employees don't realize it's a bad deal, but given that it's usually a better deal than unemployment, I don't think this is usually true.
So that leaves every other contract, and non-deceptive, non-forceful contracts are enough for a lot of people to generate a lot of profit.
The criticism here seems a bit inconsistent, or at least like the people saying profit is theft aren't remembering the criticism they're actually making. No one to my knowledge is arguing that employers are actually making employees worse off compared to not employing them, just that they aren't helping them as much as they could. If your choices are a low wage or starvation, then giving you the low wage is a better deal than starving, so it is providing something that you value. The employer is offering the employee a choice between a low wage and starvation, but isn't everyone else just offering the employee solely the choice of starvation by not offering them a job at all? At least the employer is doing something that benefits the employee, even if for selfish reasons. And it could be said that everyone else is failing to help for similar selfish reasons, yet they aren't stealing by failing to help.
If a charity set up a food bank in a poor place and people had to walk a long way to get to the food bank, the charity is offering people a choice between starvation and hard labor, but we don't say the charity is violating people's rights. The difference is that the employer benefits, but what if the charity benefits through good PR leading to better opportunities for the founders? And what if the employer didn't benefit? If an employer hired someone and then shoveled all of their own surplus value into a fireplace, that seems pretty wasteful, but now they seem indistinguishable from the charity. So if anything, employment seems as justified as charity is, just less wasteful.
I think the distinction between coercion and employment is whether you're adding options or taking them away. You can make offering anything sound bad if it's "a choice between having only x and previous bad situation" even if x is a handout with no strings attached. If I offered someone $5 a day for doing nothing, you could say I'm forcing them to choose between poverty and starvation, even though all I did was do them a favor. So since arguing along those lines seems fraught, I'd say removing options through force can be theft but offering new options isn't theft unless deception is involved. Not to mention that different people could be in different situations. If I offer Bob and Ann each $20 to do a task, and Bob is in danger of starving without the job, am I stealing from Bob and not Ann? Even though I'm making the same offer to both? If contracts are theft because of alternatives, it seems like an employer would be robbing someone by not learning about their personal situation, even if they have nothing to do with said personal situation.
If two people want to team up to do something, I'm not sure we can say the surplus value belongs to anyone unless we agree on a contract. Even if one person is doing the physical labor, surely they need consent to use the planning/design from the other person, and that kind of necessitates some agreement beforehand. Complex ideas and management may be intangible contributions, but ownership is an intangible concept in the first place, so why couldn't something intangible belong to someone? It comes from the brain, which seems like it's even more representative of "you" than the body you use to perform labor. So some contribution to a company via planning seems like a claim on some amount of the profits, and without a contract it seems very unintuitive to say physical labor, or some specific laborers, have 100% of a claim on the profits. The contract isn't really redistributing ownership, there's just no specified claim on ownership without the contract.
I also find it hard to believe employers are offering zero value if different companies perform vastly differently. If one company goes bankrupt, does it mean they got all the lazy employees? Seems a lot like a management failure, which implies the management at the other companies are doing something right.