I think the rockets should clear enough ace for Dwight Howard. That's the best fit for him. Defense would be solid, no one rebounding on them.
No one rebounds on them now. They had the second highest DREB% in the league this season.
A lot of people point to their transition play and pace as artificially inflating their offensive efficiency, but (if the synergysports data is to be believed) they were one of the most efficient offenses in non-transition offense (whether you include offensive rebounds or not). Where the Rockets were weak last season was off-ball and post defense. Per the synergysports data, they did quite well against isos and PnR ball handlers, but struggled just about everywhere else defensively (notably on post-ups, which are relatively easy to get, and spot-ups, which are easily the biggest part of halfcourt offense).
Dwight can definitely help on the defensive side of the ball, thwarting the post-ups that the sub-par stretch 4s the Rockets trotted out this year couldn't, and allowing the Rockets perimeter players to stay at home (Harden and Lin, though, are not exactly stalwarts in this regard), but he might clog things up for them in halfcourt offense (since Asik is pretty useless away from the basket...thus their use of stretch 4s this season). Statistically, Dwight has been extremely effective in pick and rolls over his career, but has gotten far more of his offense out of the post (it may be that Dwight pick and rolls are predictable since he can't consistently hit a jumper), where his results have been mixed (very poor this year).
If the Rockets can clear the cap space to get Dwight while keeping their other 4 starters (Asik, Parsons, Harden, Lin), they can probably also clear Asik and pick up Millsap. Dwight-Millsap preserves their offense (or potentially improves it) AND improves their defense. THAT could be a deadly team.