My dad just bought a sonic cleaner to use for watch/clock parts, is there any special type of cleaner or special precautions to take when using this for a gun/parts?

Brownells sells a cleaner and a lube for ultrasonics.  They work well.

I use SLIP2000 cleaner and lube.

Wipe off all oily dirt before placing in the US cleaner.  The US works much better on dry carbon than oily dirt.
Completely disassemble the parts to be cleaned, as the US cleaner will remove all old lube, and the new lube needs to reach the entire surface.
If the US cleaner has a heater, allow the liquids to heat up before cleaning.
The US cleaner may remove gun finishes, particularly if the finish is already partly damaged/worn.