For starters, there would have to be some indication that the hitch was "hit" before the insurance company is going to even consider replacing it. Then they would consider things like
a) how fast where they going when they hit you (5 mph vs. 45 mph big difference)
b) what part of the vehicle hit yours
c) is there any indications of damage to the hitch
d) Can the damage be mitigated short of a full replacement
Basically the only thing you can do is inspect it closely for damage, if you see anything point it out to the adjuster and go from there. If you don't see any damage, it's unlikely your going to get a new hitch unless you can point to something concrete and say you suspect hidden damage. After that all you can do is watch it for signs of something awry.
You'd be farther ahead to attempt to get the claim left open for a period of time to ensure there is no hidden damage. Demanding a replacement is not probably going to get you much further then a polite "sorry - we can't do that" (It's not the insurances companies first rodeo).