It's either that or white grease, wanna say white grease, that's in the M16A1 armory manual.
But after seeing how the SF gunsmith (not an armorer) assembled 'em I'd say it really doesn't matter, and I'm positive each of you puts more detail into than he did so I wouldn't worry too much about it if he doesn't. You do wanna use grease between steel and aluminum though. Or anti seize.
Not a big fan of loctiting aluminum to aluminum and never had a fixed stock or a staked carbine stock come loose anyway. The bolt in the rear of the fixed stock and the keyed portion that fits into the lower prevents it from backing out. Most of mine just get a drop of CLP or TW25B if it's around.
There is a non hardening Loctite too, green I think (careful, one brand uses green as tougher than red). But snot would probably work just as well.