Dude, if you're a restaurant owner trying to put mexican vibes out, even though your food isn't really authentic, what better way than staff it with mexican people?
Now, I don't know if by "Mexican employee" you mean actually born-in-Mexico Mexican or Mexican American... but if it's the former.... do you really wonder why they'd be working in the states...as ANYTHING? If it's the latter... that's precisely why it's tex-mex.
Seriously, the leap between a Mexican and an American of Mexican ancestry is a huge one.
Tex-Mex is the weird quasi fusion that happens in the border... music, language, food... burritos, for instance, aren't really Mexican... here in the Mexico City vicinities, for example, you won't find a "burrito" anywhere UNLESS it's a pre-packaged microwaveable one... but you'll find microwaveable pizzas and bbq wings too, y'know?
Basically... the only "mexican" food I'd say is "authentic" that I hear mentioned a lot in American media and the boards and stuff are Quesadillas. What you guys call "tacos" are... well... anything but, really.
---------- Post added at 04:20 PM ---------- Previous post was at 04:16 PM ----------
Wanna see something that's REALLY Mexican food? As in, we eat it as much as we can, it's traditional, ubiquitous and adored by everyone? The food we miss when we travel abroad?
This, my friend, is a trompo de pastor. The necesary ingredient to create our beloved tacos al pastor.
Have you ever seen one of THOSE at Taco Bell? They're literally at every other corner around Central Mexico... a bit less in the southern parts, they have their own excellent cuisine, but still a view you could probably see all around the country.