You would probably not do any damage if you dont turn the front wheels. PT4WD can function on the pavement for straight line travel, but I wouldn't do it often.
In PT4WD the front and rear driveshafts are locked together. This will cause driveline binding if you turn the vehicle because the front and rear wheels will not be turning the same speed. If traveling straight, there is little potential for binding, however if you have tires that have slightly different diameters (different inflation levels, different loading, etc), you could have some minor binding.
I dont think you would get any benefit in a race by using PT4WD versus FT4WD. You may see a slight benefit if comparing PT4WD with 2WD since PT4WD would prevent the tires from breaking loose in a hard accel.
While I am a little scared at the idea of you even suggesting this, at the fear of leaving a pile of metal shavings on the pavement.....
I dont believe the 4x4 will turn itself on whilst under great diress.... as in, while under extreme acceleration.
Someone posted this a while ago, and wanted to know if he could switch back to 4x2 while still accelerating, I dont think it can be done. Computer is too smart for that.
I have not yet done this myself. But, the big dog deisels that have there brains blown out, i.e. cpu, exhuast, turbo, etc. luanch in 4x4 to keep the 1000+ power they have to the ground with out just spinning them. I read this in a good article in four wheeler magizine. They luanch in 4x4, but then take it out of it and where running very impressive numbers - but they also have very impressive power. So I would only do this if your RREALLY need the extra traction to handle the grunt of your truck