As I said before they probably grabbed these guys to scout Schaub and now Palmer.
I doubt Skelton would provide anything of value about Bruce Arian's Offense or Todd Bowle's Defense.
Its really about the 49ers' backs were against the wall, and they needed to do what was needed to prepare for the teams ahead, rather care about the potential on the back-end of their roster.
Schaub is 6-6, 243 pounds... Skelton is 6-6, 243 pounds. At least that's what they were at coming out of college and they possess similar athleticism with Skelton being better.
Palmer is 6-5, 235... Bethel-Thompson is 6-3, 230. Skelton looks to be more similar to Palmer physically but maybe Bethel-Thompson is more similar to Palmer mentally as a QB. Who knows, note that Bethel-Thompson spent time with 49ers as an undrafted free agent in 2011. Maybe its just a familiarity thing. They would know more than any of us.
Also in case if you're wondering, Colt McCoy is 6'1, 215. Coleman is Wilson's size. None of those players can emulate a 6-5+, 230+ QB.
TURN DOWN FOR WHAT? -The 12th Man