Tamron 24-70 G2 on EOS R6: Does VC and IBIS work together?

Good news: I can answer this question for you.

Image stabilization on the stabilized RF cameras works like this. The chart comes from Canon.

All lenses used on the R6 can use some form of IS. The exact type that is offered depends on the lens.

The RF-series cameras' IBIS can stabilize along three axes: pitch/yaw, x/y and roll. Camera lenses can offer pitch/yaw (which Canon calls OIS) or pitch/yaw+x/y (which Canon calls hybrid IS). The same principles apply whether the lens is Canon-brand or a third-party lens. I can personally confirm this from owning Canon and Sigma EF lenses with IS built-in, and I've used a Tamron lens with IS (VC) as well and it works too.

Basically, the short of it is this:

RF or EF lens with no built-in stabilization. IBIS is used for all axes.
EF lens with built-in stabilization. The stabilization built into the lens is used for the axis/axes that it supports, and IBIS is activated for the axes which the lens does not support itself (but in video mode, IBIS takes priority over the lens IS for X/Y).
Only for RF lenses with built-in stabilization. The stabilization built into the lens is used for the axis/axes that it supports, and IBIS is activated for the axes which the lens does not support itself (but in video mode, IBIS takes priority over the lens IS for X/Y). In addition, the pitch/yaw correction is coordinated and so uses both IBIS and the optical stabilization simultaneously.

TL;DR. Stabilization works with all lenses, including yours. IBIS will handle axes that your lens does not stabilize internally, but since it is EF, the pitch/yaw axis will only be stabilized in the lens.