Not an offensive threat at all? I really question how much of Kaman you've seen with that statement. The guy has excellent hands, footwork, and post moves, combined with a nice mid-range jumper.
His FG% is 41%. The average for centers in this league is closer to 50%. '08 was the last year he had even AVERAGE offensive production. I will give you that he is a good passer, but he is extremely turnover prone (4.5 per game on the season, 3.7 for his career; the average center turns it over 2.7 times per game).
The best year of his career, '08, he was barely above average offensively. He has gotten worse since then. His TS% is almost 10 full percentage points below the league average for his position. That is not a skilled offensive player.
I will give you that he will look a LOT better with a PG like Rondo, and a PF like KG, along side of him. That said, I don't know where you are getting your assessment of his offensive abilities from, because it doesn't seem to line up with his numbers.