Every year at my company we are required to take a business conduct standards course that says, in no uncertain terms, that you will be fired if you do this.
The key is that you should not exchange company resources for what may be perceived as or actually be personal benefit. Outside a contractual term, set up a quarterly dinner to strategize, synchronize, assess, etc where the vendor pays? Sure! But, explicitly concede a material business term in a contract in direct exchange for a term that personally enriches you? No!
This isn't illegal. It's any two employees so it doesn't benefit an individual. And it doesn't seem to involve government contracts. What so wrong with this?
Sheesh, given that I've seen contracts signed because someone brought expensive alcohol, strippers, etc., this seems perfectly reasonable.