Manu as a 6th Man was Pop's go-to move for whenever the team was struggling or they needed some kind of jolt. And in fact, Manu becoming a 6th Man came about because the Spurs lacked a bench -- Ginobili to the second unit simply created one.
The notion that it was done for minute-monitoring came about later on. It was a byproduct of creating a bench. It became part of the rationale as the years went by and after a few injuries and long summers. But minute-monitoring isn't how it came to be.
That being said, it doesn't bother me one bit if the Spurs move Manu back and forth during the regular season. Ginobili has exhibited time after time that he's just as good a player no matter where he starts the game. And if moving Hill to the starting 5 for a stretch gets him going, so be it. The Spurs don't need to set their rotation before January and stick to it regardless of injury or cir stance. You do what you've got to do to get the most out of your team and its players.
I do believe they should stick with the same starting 4 of Duncan, Blair, Jefferson and Parker for as long as possible. Taking a long-term approach, I believe Blair needs the reps, the Spurs need his talent and 'Dyess is in the perfect role for him as a player and as a vet of 15 years -- he's preferred coming off the bench since Detroit and his minutes should decrease as Blair finds his way and Splitter gets up to speed (so Pop's able to find him more minutes).
I just don't see all that much of an issue. In a perfect world, one in which every Spurs player fulfills potential and meets or exceeds expectation, provided with the good health to do so, there are 4 players I believe could change roles, go from first to second unit, and the team may just play to its best ability: Splitter and Anderson, Ginobili and Blair.
Why is that? Because it's not about putting your best talent on the floor from the jump, it's about getting the most out of your individual talent in a team concept. And again, in a perfect world or the most ideal scenario, having a Big 3 of Duncan, Parker and Jefferson starting with the offensive and defensive skillsets of both Splitter and Anderson, you best address need and concern for both ends of the court to start and provide the type of second unit that can make a good lead grow, turn a close game into a lead or can even get the team out of the hole if need be.
But it ain't a perfect world. You do what you've got to do.
If the team needs Manu (or anyone else) to start, he (they) should. Whatever the team needs.