Does anyone know of "legalities" surrounding wait staff serving beverages in hot gles?

I don't know about any specific laws, but people do have to use a reasonable degree of common-sense when performing their duties at work. If a "reasonable person" would not do what the server did (and I would argue that they wouldn't), then that server (through the restaurant) has breached their legal duty. Given the amount of damage this incident caused (i.e. it wasn't just a few scratches), I doubt you'd have trouble finding an injury lawyer who would take your case on a contingency basis (you don't pay unless you win), if it's legal in your state. In either case, I'd argue that you have a relatively strong case against this restaurant and any good lawyer will at least offer you a free consultation which I'd definitely do.