Well FWIW I use and "age" a lot of Rawhide and have no problems getting it to dye using Fiebings Spirit Dyes.
1) Soak until properly tempered
2) while still damp apply the dye to BOTH sides - the flesh side takes dye quite well. Depending on what type rawhide you use (I prefer deer and elk (NA wapiti not the same as the elg aka moose - red deer is closest to what I use) over cow which has a much tighter grain and that makes it harder to work with) you may/will get differences in colors with splotches etc.
3) To finish (rawhide needs to be as water resistant as possible) I use what was a common finish here in the SW good ole spar varnish.
4) I don't; do a lot of distressing since rawhide when dried and finished general does not scratch easily - that's based on making them unaged and using them for years to see just what wear can occur.
You can take a look at the sheaths I've made with rawhide at www.wrtcleather.com
one caveat re: natural dyes such as coffee, tea, walnut, etc. is to be aware that they are high in tannins and if you soak rawhide in it too long it can and will tan the rawhide into leather - stiff but still leather not