Ok well, I just tested out that strangle on Ness in training mode. Yes. Training Mode.
For the most part, it seems characters with a ranged grab; mainly ZSS, Link, and Toon Link can do this without any real worries, and could probably spend a long time just mashing the grab button.. Though after a while I noticed Samus takes a little longer to actually grab Ness (like 3 grabs?) and that MIGHT give enough time to escape. When I tried with Yoshi (I might be doing it wrong), couldn't get Ness to break out without him flying into the air.
Now other than ZSS, Link and Toon Link, the worst offenders to Ness will be Marth (obvious), Snake (he does it ALMOST as well as Marth. He has to move forward a bit after each grab, but only the distance of a Force Palm chain [very little]), Squirtle (See Snake), and Charizard (See Snake again). I wouldn't get your hopes up, as I might be doing it wrong, but most other characters do the strangulation via moving after each release. Some characters require a dash after release, and if the character slides a lot (IE Luigi), it's not as useful as it would be with someone else. For example, Pit can get up to around 100% if you do it right, but since it is training mode with a level 3 CPU, chances are an actual player with spaz out and you won't get that high of a percent.
I also found it hard to do with Zelda, but I think by far the most pointless one to even do this against Ness (and maybe Lucas) is Lucario. His grab doesn't do as much damage as the other characters, and he pretty much HAS to dash to regrab again. This makes him lose distance to actually deal his half a percent of damage.
I don't want to get your hopes up too much, but with a lot of characters, this technique doesn't seem as game breaking as I thought it would be, though I'd expect most characters being able to get 30-40% before Ness or Lucas breaks out, whereas the worst offenders pretty much have free kills on grabs.
Of course I could just be doing this wrong...