Is DFT good on teemo?

I'd say no, since it doesn't proc on his E. Thunderlords helps more in lane since you're constantly harassing with autos. That being said, Fervor of Battle would be better if you're going for a more on-hit build.

45% CDR and thunderlord's is too good to pass up when you're going for full Shroom build

It works really well with both binding dart and mushrooms, both of which give you the full 4 second proc of damage. It does not interact with his poison attacks, though. So if you are primarily concerned with AP damage from darts and shrooms, then it is good for your builds. Otherwise, there are better options.

The one exception is adc teemo. Since deathfire touch has such a high ad ratio, it adds a lot of damage. But then again, if you are ad Teemo, then you are most likely in a normal game so have some fun testing things out :-)