Terrible idea: prone to politics (or complaints of same), influence peddling, payoffs, etc.
Just like a cop trying make his ticket quota can find something to write you up for if he looks hard enough, a vet can find something wrong with most any horse coming off the track.
No it depends on who claims it?
If a horse has been dropping or off a lay he should be okay-ed from the vet to race. If the sucker gets claimed and goes down in the race the damn vet should refund the money and take some damn responsibility for his over sight. After hes probably the one been given all the chit to be able to race time to pay back some of that big medical fees they charged the owner for.