Let me see if I can express this correctly. Bear with me, give me some latitude for a bit...
In the traditional format, you had a point guard, two wings, two post players. The functions of the PG was ball handling and running the offense. The wings were usually your scorers...these could either be shooters from the outside (something that gained more value with a three point line) and guys adept at slashing to the basket...that was the "original" separation between a shooting guard and a small forward. Then you had two post players who played inside mostly (post offense, elbow offense, screens, rebounds).
"Modern" basketball has gone towards offensive sets that feature four perimeter guys and one inside guy, or can even start from a five out alignment (though I think you still have a big guy who's job is to mostly set screens). With 4-1 sets, some coaches tend to divide the 4 perimeter spots into 2 guards and 2 forwards (more on that later). With that thinking you'd want the 2 guards to provide ball handling, playmaking and shooting, and for the 2 forwards to provide shooting and slashing.
There is currently a position less trend that is more prevalent in some European basketball (of course) that some NBA teams and college teams have emulated. Basically the concept is that in a basketball game there is a series of actions that needs to be done (bringinging the ball up, passing, scoring outside, scoring inside)...and that you should maximize your player's ability rather than define their roles based on height. That's how you end up with big men being the perimeter shooters or passers (also some guards as very adept post up players). The message is don't worry so much about positions as about maximizing talent and making sure you have enough of each role (a team with 5 pass only guys doesn't work).
So coming back to the RJ/Caleb backcourt. In the 4-1 sets UNC was running that year (which was a more "modern" look than Roy's 3-2 system), I don't think you need to have a traditional PG per se for it to be effective. In fact, that offense is more dangerous when you can have two guys who can handle the ball, attack the basket and shoot. So having two quasi combo guards is probably a good fit for that sort of offense...opens all sorts of options in early offense in how you can push the ball. The one possible downside? Personally, you still need a leadership on the court and having one designated PG makes it easier (rather than two guys vying for the wheel). Easier with a veteran team, more challenging with an inexperienced one.
Sorry for the diatribe...I am ramping up in my basketball season down here.