I've been at a gazillion airports over the years where, if the GM line is long & no one in Elite line, they'll take folk from the GM line. But they also will put those on hold if an Elite member walks up.

Hey count yourself lucky - you could be flying out of LAX where they merged F, 1K, 1P, 2P, *Gold, *Silver all into one line - which means GM may actually be shorter! LAX sucks for check-in now.

Cheers.