Not a good idea IMO. The universes should stay separate and I would personally prefer a different version of Green Arrow in the DC shared universe (not that there is anything wrong with this one). Not to mention that that horrible Green Lantern film seems to be in canon with the show in the minds of the creators (there is an interview where they talked about bringing in that version of Hal) which means that if MOS and Arrow are in the same universe, that horrendous GL is also in the same universe and will star in JL.
On top of that, you'll also get tons of people whining if Nolan's Batman isn't integrated with MOS while Arrow is.
On top of that, you'll also get tons of people whining if Nolan's Batman isn't integrated with MOS while Arrow is.