I never found a need to comb it. I separate the sinew and keep it in bundles of 12-14 strands, each bundle separated by the pages of a magazine. If the sinew is reduced in diameter sufficiently prior, when dipped in the hide glue, they soften in seconds. As it is softening, I dip and run the bundle between my fingers a few to several times. This squeegies off excess glue and nicely aligns the bundle in the shape of a flat ribbon before they're layed on the bow. They lay down nice, neat, and flat thataway. I dont see how combing would help any beyond that.
I don't degrease the sinew. Any grease or fatty/waxy feeling stuff seems to be on the outside, on the outer sheath which is discarded. Once it's removed, and the sinew is pounded, reduced, and separated into bundles, I simply keep it clean and dry until it's time to dip into the hide glue.
I do rough up and degrease the bow's back... and of course size it with glue prior to laying down sinew.
I LOVE the smell of hide glue.