So is silicon oil...
When I get mags brand new I'll put a drop of high viscosity silicon oil down them, load and eject 3-5 mags worth of BB's, and then wipe off all the excess.
Depending on your game climate (I've heard of feeding issues in REALLY dry and sandy areas being fixed by a bit of lube in the rubber) it'll matter what you do/don't lube.
In Manitoba I have never lubed anyone's hop-up rubber and as long as they use decent BB's they do not have a single feeding problem.
Gun Technician and Tuner
Well versed in every AEG version and all major gas and spring systems.