Rat quarintine question?

It'll work, short term, as long as the hamster size cage is not a habitrail that has those plastic tubes. Rat feet can get caught and broken in those tubes. Make sure they each get outside the cage time. Also remember that it takes a couple of weeks for the neutering of the male to take. They are still fertile when they come home from the vet, so the separation will need to last for at least 2 weeks after the neutering.