That's interesting.....I'm in sort of the same situation but only work PT at a vet's office and volunteer weekly at 2 other places (also vol at 2 non-animal-related places) in addition to taking classes PT. When I talked to Cornell about my app after I got the rejection, Jennifer didn't even mention my PT student status. She really emphasized diversity in animal species more than anything else, and even mentioned that short of getting another degree I wouldn't be able to bring up my cum GPA (3.3) and agreed (I think) when I said that it sounded like I should concentrate on animal experience more than classes for my '08 app.
I'm sure every school has their own priorities, but just thought I'd throw that out there. If I have to talk to my other schools (still waiting on WI, TN, and PA), it'll be interesting to hear what they have to say. What schools did you talk to that didn't like PT students? (And sorry that I don't have an answer to your question....my assumption would be that they think FT students show that they can handle the workload at vet school, but it would seem to me that juggling job/vol/school/everything else would demonstrate that just as well).