Besides the legal issues, would I have problems with my service engine light or any sensors if I removed it from a 2000 silverado 5.3?

If you remove the converter, the SES light will come on for low catalyst efficency.
If you are looking to decrease exhaust back pressure removing the converter will have no real effect.

Is there anyway to override the SES light from the removal of the cats?

I dont think there is any way to override the light. Seems like it would help flow to me especially one that has a few miles on it,then they have a tendancy to break or melt down causing a resriction. If removed your engine will most likely run richer than normal.