Since it would make sense for DC to continue collecting Green Arrow directly from the Grell material, I'm with FlashingSabre, they won't do it. Maybe they'll start immediately with Dixon's run, which would make little sense as a jumping on point since Dixon's run picks up ongoing storylines from other writers (it's literally part 3 of a 5 part story, and directly follows from what they'd be doing with Oliver starting with Crossroads). That would be more DC's style- organizing by creator in such a way as to make things difficult to read and missing parts of stories (New Teen Titans Omnibus Vol 3, all of the Legends of the Dark Knight/Tales of the Batman books organized by artist only, collecting only the Messner-Loebs issues of Wonder Woman that Mike Deodato drew, etc.)
Though I am given hope by the fact that these Green Arrow by Grell volumes are just called "Green Arrow Vol. #" and not "Green Arrow by Mike Grell"- that does seem to indicate a willingness to continue the series proper. They've made great strides in what they include in their books over the past couple years, so it's totally possible. But DC is nothing if not a "one step forward, two steps back" kind of company when it comes to collected editions, so who knows what'll happen? Having just read from Crossroads and being currently up to Meltzer's run, I sure hope they just keep going sequentially. It's great material and worth a reprint for sure.