I've seen plenty of false LOC indications but not very many for the GS.
Our SOPs don't restrict whether you capture from above or below.
I'd have thought being on a 6 or 9deg glideslope would make the subsequent approach 'interesting' in terms of stability, unless your aircraft type was designed for it, like those that go into LCY (5.5deg).
As other posters have said, there are many ways to check the authenticity of a GS (RoD, height vs. distance, etc.). It doesn't strike me as particularly dangerous (unlike a false LOC), as it will be difficult to follow and actually give you increased terrain clearance. Probably not a good idea for sub-CAT-I Ops, though...