Is it possible to combine geotag images (from the UAV) and non geotag imagens (from de ground) in the same project?
Yes.
Yes, but I have recently seen many problems, which I never saw in previous version. The most common problem is that Pix4D fails to calibrate ungeotagged images and are invisible around the data framework, I suspect they are thrown away to near 0,0,0. For now I just make sure everything is geotagged.
A couple of manual tie points shared between the two data sets should knit them together, even better if you can geotag everything.