Certainly not taboo! Another place to look is
www.voicebank.net.
It's a great place to hear 'the best of the best' in
VO and get a list of both union and non-union agents.
Different agents seem to provide different things. I have one agency that sends out great leads to a group and it is up to you to book the job with a great audition. I have another agent that is wonderful at getting me work(I am her go-to 'teen' and 'no one else can do it, call Kara'- girl). Finally, I have a new agent I am just becoming accustomed to and still learning her style.
Recommending names might not help- you may have a completely different experience. I also go for the non-exclusive thing. Unless it is a top agent that will supply you with tons of work, you need to protect yourself.
Good luck!