I'm sure people will disagree but based on the way he talks about drumming . . . I don't think he feels the music at all . .. if a song is in 6/8 he's thinking of all the ways he can subdivide 6 over 8
and split it up between limbs and tonal variations.
I've never heard him say anything like " Well this is a medium 5/4 feel so I just laid down a backbeat and just grooved along with the song "
It's pretty much always " Well the song is in 5/4 so that means I can play 3 over 16 with my feet and 2 over 4 with my hands and swap over every 9 bars ... "
See, this I think is a misunderstanding and is going the way of a caricature.
Mangini does not really consciously count when he composes and plays drum parts. "The numbers are always in my head," which means the counting is already intuitive out of a strict practice routine. Instead of conscious counting, he sees patterns (or shapes as he calls them) where he can visualize how these patterns fit into the overall structure of a song. A good example here is the intro of Surrender to Reason, where he did different versions of the fast roll, and one of them clicked with James LaBrie as the one that is best to use, and it was only afterwards that they counted it as an odd-metered roll of a 29 over 5 polyrhythm.
When he gives interviews and explains in numbers, though, that is the teacher Mangini trying to explain to the lay person (or to the ordinary drummer) what he is doing. You can not tell a student "just groove along" "just feel it" or something like that because it does not mean anything. But when you explain in numbers, that is, you tell the student to play this then subdivide to so and so, then the student will understand what you mean and know how to play it. That's why he always comes off as if he is always counting when he does the interviews. He wants people to understand what he means.
About the groove thing, I think it's really largely a function of not getting used to listening to polyrhythmic drumming. I mean, I hear the groove in a lot of Mangini's drumming, but I think it's because I am exposed to polyrhythmic stuff as I am immersed in world music. Latin drumming, for example that of Horacio Hernandez which Mangini pointed to as a huge influence, has a lot of those polyrhythmic stuff that some might consider un-musical.