The LMB X SMB hybrid is pretty rare. The SPB X SMB mean mouth is much more common. Table rock in Missouri and Dale Hollow and Watauga lakes in TN all have them show up at least occasionally if not regularly at tournament weigh ins. I've spent the last 25 years bass fishing in waters with smallmouth and largemouths and I've never seen a cross between the two. LMB spawn much shallower than smallmouths on highland reservoirs, but spots spawn deeper like smallmouth.

If you have spots and smallmouth you will definitely get meanmouths. I have personally caught one and seen 3 or 4 more that I know of.