I've got an older Leupold M8 6X with markings on the windage and elevation knobs that I'm not familiar with. They're incremented in groups of 5 starting from 0 - 35. Does each increment represent 1 moa?

Yes - that's what they are supposed to represent; Leupolds are notorious for these being somewhat imprecise. They hold zero well, but it's sometimes a real chore getting them zeroed.

Don't worry about the marks, just follow the crosshairs.