Should I scrape out portobello gills to avoid sogginess? I am not worried about the dark staining of everything else on the plate; rather, keeping the caps from going soggy.

Yes, a hot pan and a bit of salt helps, but does scraping make much difference for sogginess if the gills are newly opened and rather dry? How about older, moister gills?
From my online research, I don't think that the gills themselves have an impact on the texture of cooked portobello mushrooms.  It appears folks scrape them to avoid the discoloring issue that you mention, and also to remove any potential grit that might be captured within. Why not try an experiment and report back to answer your own question?