Some landlords ask for a vet's record of Frontline treatment plus a desposit to pay for any damage caused by the cat/s after the tenancy finishes, OR some just hate animals and won't have them at all.
When the landlord is a vet who doesn't allow a tenant to have a pet, I'd say he has got nothing but pound signs in his eyes, so I wouldn't be renting from him and I wouldn't be using his vet services in future either.
While some vets start off full of compassion for animals and live within high ideals and provide brilliant services, others forget their early motives and just become business people. We in Canterbury have recently had to deal with vets who have outrageous policies aimed at bringing in more cash in direct conflict with the needs of the animal in question at the time. One vet wanted to charge a member of the public £10 to show her how to set one of our borrowed traps properly when she was trying to catch a puss in danger. Pathetic, really, isn't it?