Yes been running dungeons with them. My playtime is limited but I'm at ilvl 375-385~ on the whole team, somewhere in there. With cooldowns popped, I sometimes see 17-20k DPS on a 30 second fight but will go down to about 12-13k typically. On movement heavy fights expect 10k~ ish.

Boomkins can also heal extremely well, Regrowth with resto affinity does not take you out of Moonkin form, and you also have swiftmend / Wild Regrowth / Rejuv as other heal options.
Since they are ranged they typically don't take as much damage as melee, so the passive 3% heal x4 is active on your tank the entire time making that character need less heals.

Treants are insanely OP for trash, it's a free tank and damage absorb for 10 seconds. You got 4 of them every minute.
Boomkins suffer on two front, their damage has a slow ramp to it, and movement really hurts their damage. Other than that they are amazing.
If you can handle the style of 4 ranged and a tank, this is a solid choice. You still get essentially 5 DPS and stuff drops way faster than the usual 3 dps /tank/healer combo.
Your missing a dispel because there is no true healer, but there aren't too many places that's a deal breaker.
I want to say I've done a +5 with this team but I can't remember, I haven't pushed myself on it. I did a +2 motherloade last night and 2 chest it, I wiped on the first boss due to bad play on my part.

You can do this with a bear tank, they just take more damage than a DH, and have less self heals.

As for avoiding mechanics as ranged, it's a lot easier than dodging as melee. You just need to make a few extra keys and get used to it, such as a movement key for forward/back/strafe left/strafe right for all boomkins. As well as a spread out macro.
Example: first boss in Freehold. Stack the team and fight with the tank somewhere else. He'll charge one of your boomkin, strafe left or right on them to dodge. He goes back to tank, on second phase split your ranged with a spread out macro and continue to dps, once the green goop hits someone (it only hits one if spread out) swap to that character and move out, then keep dpsing.