Can you ground an outlet by wrapping a wire around a galvanized pipe that is attached to plastic pipe under the house, or does the pipe have to be in the ground ?

Absolutely NOT!

Only in very rare instances can a pipe be used as an equipment ground source.

The earth has nothing to do with equipment grounding either. So a ground rod or pipe is a useless source of ground as far as this goes.
The earth serves a completely different purpose.

Does this pipe ever make an unbroken connection back to your main without any plastic interrupting the run?

Does this pipe ever make an unbroken connection back to your main without any plastic interrupting the run?The ONLY place a pipe can be used to make an equipment ground connection is within the first 5' of where it enters the house and IF the pipe is being used as a grounding electrode, with a proper connection to the main panel.
The key is the proper connection to the main panel.