Sorry, I keep asking all these serious questions!!! But I was just randomly wondering... 
Does MIDI velocity compensate for changes in velocity? Like when one track is louder, does it soften all the others to not overblow?
(Mainly/only in terms of General MIDI?)

No, it does not.
It is vital to keep an eye on your synth audio outputs. Many synths tend to run a little hot on the output.
It is important to understand that velocity and volume are not the same thing.
In most cases, velocity will impact the timbre of a note. It also affects the volume.
However, you can reduce the output level of a track without compromising the effect of velocity on the input.
Watch your meters, especially the master bus. If it's clipping, dial the individual tracks down.

I find I have to turn most synths right down to avoid the ProChannel overheating. Look at Z3TA for instance...when I go through the presets, looping a MIDI clip whose notes average a velocity of about 96, the ProChannel goes into the red unless I turn the volume down to about 20%. And if you're adding things like tube saturation it becomes even more vital to turn the synth output down. 

Not sure I understand your question, davdud101 - are you saying that one loud track is making the others seem softer? Maybe it's just an aural illusion, i.e. your brain is tricked into perceiving the quieter tracks as having softened, in relation to the loud track?

Look at Z3TA for instance...when I go through the presets, looping a MIDI clip whose notes average a velocity of about 96, the ProChannel goes into the red unless I turn the volume down to about 20%. And if you're adding things like tube saturation it becomes even more vital to turn the synth output down.

This is what the Input Trim  (Input Gain) is for on the channel strip.  On any mixer the first control in the chain is input gain so that loud or quiet sources are all "normalised" to roughly the same level before any further processing.
 
Don't turn down the output of the synth,  turn down the input gain of the channel.

Yep.  The girl lady is spot on again!

That's a good point, I don't take enough advantage of the trim control.