I work for pizza hut so I can give you some advice!
The dough and meat toppings are kept frozen instore, veg toppings are kept refrigerated. Officially speaking, I really dont think you should freeze something once its been cooked then heat it up again once you've defrosted it. It's possible this would lead to food poisoning, especially considering that all the dough pizza hut use has already been frozen and defrosted prior to you buying the pizza so you really shouldn't refreeze it.
Unofficially, maybe you'd be alright, especially considering you wouldnt be eating any meat. Personally speaking I wouldn't do it, but its your decision at the end of the day!!!
Also I hate to boast, but working for pizza hut you get to eat a lot of pizza on shift!!! It sounds good and it is at first, but its too hard to resist and very easy to put weight on. Depends on the pizza hut you work in as well as to whether you're allowed to eat pizzas which are not needed.