Are you talking about tube PA amps that have the 70 and 100v line outputs, or are you asking if those line transformers can be used on a tube amp?
The answer is basically yes in both cases, but you have to evaluate the specific transformer in question. Two of my best tube amps started life doing PA duty. There is an un-used 70v and 115v tap in there.
Mike has designed several very cool tube amps around fairly inexpensive PA line matching transformers.
Solid state amps often have a transformer inside to step it up to the 70 or 100v line. Often you can get a normal 4-8 ohm output by bypassing that transformer if it doesn't have a connection there already.