Many of our bikes already have a battery tender pigtail sticking out of the side of the bike. Since this is attached directly to the battery can it also be used to power our heated Gerbing gear?
Fused and gauged appropriately yes it could. Input or output (i.e., from the battery tender or powering the clothes) it's still just a connection to the battery.
Gerbing itself at least used to make an adapter cable for this. Just looked on their website and didn't see it now though. Might be worth a call to check further.
Another option is eliminating the little dangly pigtail for the battery tender entirely and going to a conveniently mounted hard point. A company called Powerlet offers lots of options. They use the almost ubiquitous BMW type power plug. Adapters are available for that plug to just about anything so you can use the power point for you tender, clothes, chargers, etc etc etc.
I've got one on both bikes. There's a relatively convenient mounting hole that works on the baggers and is accessed through the empty area in front of the battery. The hard point is handy and having the fixed point right under your left legs works well for the heated clothes.