When I work portable on Kahoolawe, I zip tie my EARCHI vertical (with fiberglass kite pole to support the wire) to a 6' tall pipe embedded in the ground.  My question is, how does the pipe affect transmission from the antenna?

It depends on how far your antenna feed point is from the metal pole. It may cause some detuning but I doubt it causes any major issues if your antenna works  and has resonance on the bands it was designed for. Proximity to ground causes some ground losses anyway.
I may be wrong but there are a lot of variables involved to make any conclusions. Have you tried using the pole as a grounding rod? Maybe connect the coax shield to the metal pole?