OEL is always an interesting name to toss around but, even in his stronger offensive seasons, he was a high Minus player at even strength. I'd be a bit wary about just how good his impact would be with the Habs.
The idea suggested that they would take Domi back is ridiculous, IMO. Drouin and Fleury for OEL? Really?
I agree with those that see ARI throwing in the towel on the present if they agree to part with OEL. Montreal could surely acquire him without parting with their current core. It would take the 16th OA this year, for sure, maybe Norlinder or Romanov and Caufield as futures, to round things out, with Romaniv being more appealing to ARI because he's much closer to being an NHLer.
Personally, I don't see OEL turning Montreal into an instant contender -- because we need scoring up front as well -- so, giving up Caufield would be a bad idea in a trade for a veteran D.
The only positive about OEL's c0ntract is that the term is eaten up after a season played at age 35. Odds of getting maximum value for him are much higher than a long term contract that would have taken him to year 40, like Weber, for example.
It really would depend, for me, whether Montreal can make other significant moves to improve their situation up front? Domi or Drouin for Samuel Poulin, plus a 2nd rounder might be an interesting gamble to improve our size up front without losing out too much on the talent situation. However, with such a move, I'd then want to hold on to Caufield because Poulin would help surround him properly on an offensive line of Poulin - Kotkaniemi - Caufield, for example.
IMO, there are better trade options that won't plunder all your best prospects and your 1st round pick and still upgrade the left side of D for Montreal. The GM will just need to be more creative than he would have been with a traditional hockey trade for EOL.