If you are an employee of United Technologies Corp you won't have an issue. If you are not, then they may remove the discount and charge you the walk-up rate. Or they may not. It really depends on the agent checking you out and how much the local office enforces that sort of thing. There is really no definitive answer, and anyone who tells you that they never ask at location XXX is giving you wrong (or at least incomplete) information. It's very much a YMMV situation.

We can tell you that certain Avis locations in Manhattan have a sign at the counter that states that you must show ID when renting using a corporate discount number. We have seen them ask. Does it happen elsewhere? Yes, it can. Will it? Hard to say for sure, but better safe than sorry. Use a discount code you actually qualify for.