Yes, SpywareTerminator was previous affilated with IBIS, a notorious distributor of adware programs such as WinTools, WebSearch and Huntbar. However, the vendor had announced that it was exiting the adware business. So far, research on the product and its vendor's behaviour has warranted no serious problems.
Here's a very enriching discussion (with a little spice):
Spyware Warrior :: View topic - Spyware Terminator
Another discussion here:
Spyware terminator is it good ? - Wilders Security Forums
ClamAV is a free
open-source anti-virus product, and it's widely-used. And yes, Spyware Terminator has an option to install ClamAV as well, I see no problems with that.