Kcoughli,
Yes. This came as a big surprise to me as well. My adviser at NCSU (director of LAR, and himself in charge of resident selection for the RTP LAM consortium residency) informed me of this when I began hitting him up for info. This expectation (for SA general practice experience) isn't adverised. Program directors, however, do apparently have a distict preference for applicants with this experience under their belt.
LAM is different than general practice- you're right. My adviser harps on the fact that you can't be a good lab animal vet until you're a solid generalist first. This is his opinion, and apparently the inclination of other heavy hitters in the field.
As I mentioned previously, not all LAM residencies are treated equally. My adviser did admit that many folks are admitted to LAM residencies directly out of vet school. For some programs, however, if you're competing against applicants with general practice experience, they'll have the upper hand (regardless of how much research experience you have). This info was confirmed by current residents with whom I spoke at this year's NC Workshop in Lab Animal Medicine (where the mock ACLAM board exam is administered).
I'd hit up the lab animal vets at your institution and get their opinion on the issue. In summary, you can get an ACLAM residency without general practic experience, but you'll be more competitive if you have it. Given that some programs will have multiple applicants with that experience, it becomes a defacto requirement.
Hope this is helpful.