A lot of Nascar race winners do burnouts at the end of races. In fact, Nascar 09 allows you to do burnouts if you win a race.
Of course, Nascar isn't exactly the most civilized type of racing and doesn't generally have the most civilized fans, but it is a professional racing league. If it's widely accepted there, it should be accepted on Prologue.
Of course, if someone is a complete jack*** and rams his way to a 1st place win, then a handbrake finish is like a huge middle finger to everyone else. If a racer wins cleanly and there's no chance that the E-brake slide will interfere with others' finishes, I have no problem with it.