Non-competes are restrictions on employees by their current employer. A non-compete agreement between a seller and buyer is perfectly fine.
A similar thing is often done during dismissal: sign away your rights to sue for wrongful dismissal in return for severance. In my case, almost a year's worth of pay seemed like a reasonable severance, so I took it and didn't argue.
Well, it's up to market protection agencies to look at the specifics.
I think the operative principal here is that employees are at a disadvantage w/r to employers. Buyers and sellers are not presumed to be at any disadvantage w/r to each other.
Anyway, that's not related to the employees contracts.