Just after some straight answers... The company selling a
commercial license to the GPL software is obviously motivated to
sell me one, as opposed to help clarify the GPL.
What do you mean with a commercial license? The GPL is after all also
a commercial license. Is this license incompatible with the GPL?
Maybe you could get a deal on a license that is compatible with the
GPL from this company.
Also, are there lawyers that deal with this sort of thing
specifically?
Yes, copyright lawyers.
It seems quite difficult to get straight answers on what exactly
is/isn't ok with the GPL...
Try reading the license, it is very clear even for non-lawyer people.