Water tote for indoor pond?

Yes it would work fine, but you may need the cage if cutting it down. Just make sure you know what was stored in it before, so you don't poison your fish due to some lingering residue.

Do you want to cover the the entire top or just something to hold the light?
If you want to just put something on top to prevent escape you can just use light diffuser panels. Then secure light to cage. Click link in my signature and you'll see how I built a thermo cover for my 180 using rigid insulation boards. There are a ton of ways you can accomplish these things, just gotta use some imagination.

My employer will be selling these sometime in the next 6 months for 60$. The ones we have come in containing a vegetable oil based lubricant for our production lines. Been drooling over them since I heard about it.

Looking at that thing, I was thinking that if you cut the top off cleanly you can just reuse that top as a cover.....and just strap some lights to the underside of it.

just rest a 48" fluo fixture on the cage top.

I wouldn't cannibalize that container. IBC's like that sell for about $400 to $600 new. So buy'em for $60, sell'em for $200. They're worthless once you cut off the top.