An airfield which only has cleared and graded areas and obstacle limitation surfaces for visual flights can accept IFR flights however, they must be visual since there can not be procedures for approach in IMC unless the appropriate obstacle limitation surfaces are in place.
Operators using such places will have appropriate defined ceiling and visibility minima in the ops manual.
Put in a slightly different context which may explain things better - there is no requirement to use CAT 3 hold points and LVPs when the weather is at Cat 1 minima.
Cap 168 and Annex 14 are tyhe best places to look for the exact info.
Regards,
DFC