Only variant that is different from original mob should have spawn egg variants. 
OK: vex-> guardian vex, allay -> build allay, blaze -> ghast sister, frog -> cat(because they are different mobs)
NG example1: cat -> winslow/gray tabby/dyed cat (because they are variants within one mob)
NG example2: warden, polar bear, sniffer, strider...(because they are simply costume change)