Actually, you can. You can't use them for anything that requires a level (synchro, ritual), but Tribute summons and most tributes as cost are valid.
"Wowwww, deeeeelicioussss!♡"Furthermore, we sacrifice the A5-Rank Japanese Black beef..."Wowwww, sacrifiiiiiiiiice!♡"How do you like your A5-Rank Japanese Black beef?...and summon a Silky-Haired Blonde Dragon!!