Mummy needs flash in order to be less unsafe in the jungle.
I play udyr most of the time. When I see a smite amumu without flash, all I have to do is to rush the small golem (to get lv2) and ghost to him from the entry closer to mid lane and then bear him in the bush, and then tiger him to death...anouncer: first blood. The only way for an amumu to escape this is to flash to the second row tower right after the stun ends avoiding the tiger proc.
Amumu is certainly not an OP jungler, he is too easy to be countered. (Same with other must-start-at-blue jungler who doesn't get their CC skill at or by level 2)
Just don't play at 500 ELO or below ... Everyone that's half decent covers their jungler. so if you go gank him at golem you WILL die.