I think he's currently one odfthe worst junglers, his skill set doesnt support the jungler's ganking, he's slow, the CC works only when he's nearby enemy champs. unlike Lee sin or Maokai that can get up on your face from out of nowhere, then slow you and deal tremendous dmg (in the case of lee) and still keep wonderfull positioning (in case of both lee and maokai) because they can dash to a location and disrupt your scape, Skarner's only usefull tool is he's ult and he doesnt have it till lvl6.
Maokai its very much viable for jungling, and his ultimate is very useful to tank Baron and dragon and keep the damage your team takes in very low lvls