I bought a factory threaded 10/22 rifle as well as a MK22 threaded pistol from Ruger. Will they work with an AAC Element or should I have the threads checked to be concentric? What's the washer on the front of the 10/22 barrel behind the thread protector for?

10/22 factory threads are often sometimes longer than is desirable and require a spacer.

Probably need a picture or at least a description of the washer unless someone is already familiar with it.

MK II ? MK III ? Kind of assuming 22/45 ... maybe a LITE? Should be fine with the pistola.

I got a Gemtech spacer for my threaded 10/22 take-down from my LGS.

I have an AAC element can. The rifle came with a washer nut type of thing that's behind the thread protector. Could I safely run my can on the rifle and pistol? Will the Gemtech spacer work with the element and factory threaded 10/22 and mk22?

Considering the investment you have in the Element, it seems to me you'd be well served taking the precaution of taking the guns and suppressor in to a qualified gunsmith and having them checked for alignment. Optically and probably better to use a true steel rod as well, something smooth and just a hair smaller than the bore, to see if there's any offset in suppressor alignment. Just because a barrel is 'factory threaded' doesn't guarantee alignment with the bore of the threads or the shoulder.