Assuming you're looking at the glass tile inlays. Yes, I used conventional cementitious grout, but bear in mind that it was unsanded on top of plastic laminate, not stain & clear on veneer. Thus not a problem to sponge off and polish. I suspect one could do it over stain & clear but I'd mask it off and make sure finish was good and cured, not just dry to touch.
Yes to self alignment, the technique kinda depends on that. Since I did these, even stronger N52 neodymium magnets are commonly available. My current favorites are 1/4" diameter, in either 1/4" or 3/8" length depending on application. Sometimes 3/8" in cabs and 1/4" in grill so they can be slimmer in profile. Don't want to bury to deep in either, but the magnetic force along axis is pretty amazing!
I'm fond of doing grills with the larger hole in grill as shown as alignment is perfect every time and orientation of magnets is not critical. They "self-correct" in a very obvious way. You can see more of the same using N-52s in my X-Otica build thread.