Light Aircraft Association

Ready the requirements it says

If a navigation radio is fitted, and the primary display of navigation guidance is via a single complex instrument, a secondary display of guidance information shall be provided.

If there are other means of Nav guidance is by GPS presumably you do not then need a back up display of the VOR/ILS?

That sounds like they mean using a VOR receiver and display using an EFIS rather than a dedicated CDI/Glideslope.
The SL30 can display From bearing or CDI on its own display, so presumably that would be an acceptable back-up to the EFIS display (though not for glideslope).