According to my word processing system (Microsoft Word), my personal statement is 749 words, but out of curiosity I pasted it into the VMCAS personal statement field, pressed the save button, and it did not give me that annoying "please limit your personal statement to 600 words!" message.
After playing around with the field a little, it appears that it is set to accept 5000 characters with spaces, which may average out to 600 words for most (now I'm worried that my statement is comprised of too many short words!).
I think that as long as your statement fits into the field, vet schools are going to read all of it...I wouldn't want to attend a school where the members of the admissions committee are actually anal enough to count each individual word!