Sorry, quid, but you have it the wrong way round.
Crossing the Inner Marker you should be at 100'. You don't use the marker to confirm your height. You use it to cross-check glideslope indications, the same way you check your height (or altitude when operating QNH) crossing a locator NDB or at a 4 DME fix, or whatever.
You should not under any circimstances whatsoever use any variety of "fix" heights/altitudes as accurate indications of azimuth position when flying a Cat II/III approach. In LV approaches, everything works off the RadAlt. If that is inop, then LV approaches are not authorised.
Conversely, on Cat I approaches everything is off the servo altimeter and you may not use the RadAlt for DH.