Yay or Nay? I found him doing pretty well as a support seeing as he has a solid root, a mini knock up, free 35 second visions sapplings, and an a AoE damage reduction ult. That kit doesn't sound too bad to help support your jungler ganks. The downside is that he's a Champion you have to be in their face compared to many other legit support heroes whose usually in the back or near their AD Carry. Meaning he would need some source of income to get some decent items to enable him to be in their face. The way I usually tend to fix that is farm lanes when my team is backed. Not to mention you have those 5 per 10 gold items to help your source of income. With mana cost visions you won't have to invest too much into wards.

Well you might say he's better as a jungle. Without a doubt he's a pretty dam good ganker/jungler in my opinion. Though if he has such a nice kit to gank, why not have that with the additional jungler to help gank for bot lane? Usually you end up making your enemy back up which let your AD Carry farm carefree as you're dominating a lane. It all is based on what type of team comp they have and what type of team comp you have. It doesn't always work 100% of course.

I usually never run out of mana even with a few tosses of sapplings in vital places for the enemy jungler to gank. It ends up shooing enemy jungler away which leads to hopefully winning your lane.

I'm mostly talking hypothetically, Maokai usually either as a jungler or support he is depended on his team. Without a good team, Maokai can't seem to really pull in successful ganks. Either way do let me know what you think about Maokai support if it's a decent role. :]