CSU told me directly that WICHE (from AZ at least) is just as competitive, if not more so, than OOS. There are only x number of seats for WICHE (from each state) and quite a few people applying for it. You aren't just competing against the WICHE applicants who applied via WICHE at CSU, you are competing against all WICHE applicants for all 4 WICHE schools (CSU, OSU, UC Davis and WSU). So the competition is 4-fold because it is competition from multiple schools. This is also why WICHE highly recommends that you apply to all the WICHE schools as it increases your chances of possibly getting a seat.
So, when you apply via WICHE to CSU you aren't competing for just the seat(s) available at CSU, you are competing against all available WICHE seats among CSU, WSU, OSU and UCDavis. Last I checked, I think AZ has somewhere around 5-10 WICHE seats available each year for vet med and there is no number put onto how many seats a specific school will have, this is in total among all 4 schools.