My Robin Mather SS MTB frame has steep seat and head tube angles - can't remember what exactly but Robin did raise his eyebrows and ask if I was sure at the time. Love the bike as it climbs well for me that way.
In hind sight a slightly less steep head tube would have been sensible for descents but it's entertaining and super speedy in sweeping singletrack...but I digress.
Recently bought a Dialled PA and this too appears to be steep angled compared to some other frames out there (coming over from an Inbred and comparing Soul and P7 before purchase) and again I particularly like the way that climbs.
Also had a Pompino in the past and that felt great running SS/Fixed on and off road but then the seat tube angles probably not that different to my preferred HT MTB geometry.
So I think it does not matter really if it is SS or geared but more what you like or you are used to.