I would say yes, but the only thing effected would be the magnitude of the immobilize. The mag of 1 DS for controllers is already 20. 20 is more than enough to stop any AV in it's tracks, so 2 DS stacked on top of each other won't really make much of a difference. With DS enhanced with recharge, it should come back in 20 seconds, so 2 grav controllers and a group of melee players could keep 1 DS active permanently by alternating and the melee players would only fight inside it's area of effect. Sounds fun actually lol!
When used properly, DS is a great pacing tool that doesn't need enhancements. Range is already nice, doesn't cost much endurance (it's only active for 20 seconds), can't extend the immob duration (did I mention it turns off after 20 seconds?), 100% accuracy. Throw in a lethal damage proc from an immob set or add a recharge IO and call it a day.
The best feature of this power is that you can deactivate at will, which is different from other single target "phase shifting" control powers where you have to wait the duration.
Can anyone confirm how many enemies DS effects?