Roy has above average court vision and passing for a shooting guard. Bayless may have below average court vision and passing for a point guard. I'm not convinced that each player needs to be the platonic version of their position, so long as the "right amounts" of passing, scoring, rebounding and defense are there. In terms of court vision and passing, if Roy's above-average-ness at his position makes up for Bayless' below-average-ness at his, that seems like a fine model to work with.
I think distribution of "point guard" duties over both guards can work fine. Neither Bayless or Roy may be ideal point guards, but if they can both play-make to some extent, I'm willing to believe that that will be equivalent to the "traditional" model of a point guard who largely handles all the play-making duties and a shooting guard who doesn't do much distribution.
I don't think who specifically does what is the key. I think the key is that the team, overall, has all the things it needs. In an extreme case, if the team gets 10 RPG from its shooting guard and its power forward gets 4 RPG, I don't think that's a problem--all that matters is that the team gets all the rebounding it needs. In the case of the Blazers, I think the team will get all the passing it needs, as Bayless and Roy are probably at least average for NBA backcourts in terms of passing and Aldridge and Oden are probably above average for NBA front courts in terms of passing. Not having a classic point guard doesn't seem like a major issue.
As far as I'm concerned, the guard who plays alongside Roy would ideally have the following qualities:
1. Defends point guards well
2. Knocks down shots from the perimeter at a good clip
3. Slashes to the basket and finishes/draws fouls
4. Dishes to teammates when defense collapses on his drives
All of these things I believe Bayless is capable of. He has the tools and desire to be a good defender, he shot the ball well outside his sporadic playing-time rookie season, he showed an elite ability to get to the hoop and draw fouls even in his otherwise poor rookie season. I think he showed the passing ability in college and in summer league to find teammates off defensive attention he draws. He doesn't have the passing skill/court vision to initiate the offense on the wing or at the top of the key, but I don't think Portland needs that out of him.
