Yes, you should be able to connect any animation to drive the whole body animation if you have your character exported as usdSkel.
if the character head mesh has matching topology to the head mesh in the usdSkel, then you can simply select the a2f driven head mesh, then the head mesh in the USD skel, and use Toolbox>>BuiltIn>>Mesh>Connect Points
It applies to other meshes on the face like beard if you have them driven using wrap.
This similar workflow in this tutorial How to Use Audio2Face in NVIDIA Omniverse Machinima - YouTube
Difference is that if you want to keep Audio2Face live, then you do everything in Audio2Face app without exporting the result as Cache.
If your A2F driven head mesh has drifferent topology than the one in your usdSkel, for example, the head is cut off in A2F, while the usdSkel one includes the torso as well, then instead of using the ToolBox Connect Points, you can drive them using the WrapUI instead and enable the maxDistance so A2F doesn’t affect the rest of the body.
Hope it helps.