I thought Knowsley Safari park were planning to house hyenas at some point?
Are the Aardwolves at Twycross and Hamerton related? I know Hamerton bred from theirs some time ago. I'm sure other european zoos still hold some but they are not listed on ISIS.
While there is still a need for African Wild Dog holders, I doubt Hyenas will make a big appearance in the UK, certainly the safari parks are more likely to acquire them, in particular west midland seems to go out of its way to obtain species not necessarily recommended by EEP coordinators and ESB holders.