The fact of the matter is that the HEST won't be affected at all by remaining with you at work. It's a beast of a knife and will hold up just fine even in semi-moist environments. I take mine fishing all the time. Additionally, I don't really suspect that your other blade rusted due to work-related aerosolized fryer grease exposure. It's more likely getting a bit of corrosion from your body sweat or airborne moisture. That being said, any such corrosion on an ESEE blade will likely only be superficial and cosmetic if the blade is properly cleaned and oiled regularly.
But the real issue for me is that a 20 year old bringing a HEST into work at a burger joint is just asking for trouble one way or another. Ever heard the Cash song "Don't Take Your Guns to Town?" The ZT seems a bit overkill to me as well, but I'm not a big fan of recurves, or ZT knives for that matter, so I'm biased.
Anyways, I don't mean to sound like your dad, but it doesn't make much sense to bring the HEST to a part-time burger joint, unless that's some monster damn burger you're flipping!
I recommend a solid pocket knife like any one of these:
http://www.knivesshipfree.com/Great-Eastern-Cutlery-457
They are stout as hell, durable, fit nicely in the pocket, will get scary sharp, and will serve 99% of your needs at your current job. Do what you want, but leave the HEST in the truck or at home - just my opinion.
The last thing you want is some jackass kid or dope head grabbing your knife from you while you're busy working in the fryer or something and doing something stupid with it.