May a VFR-only pilot without high-performance or complex endorsements be the safety pilot for an IFR currency flight?
First, can a pilot without an HP endorsement act as safety pilot in an HP aircraft? Since 14 CFR 91.109 only requires a safety pilot to have category and class ratings, there's no need to have any additional endorsements.

That's confirmed in this FAA legal interpretation:


  there is no regulatory requirement that a safety pilot have a
  high performance endorsement to act as safety pilot


The same document says that safety pilots are "encouraged to be thoroughly familiar and current in the aircraft that is used" - which is great advice - but that's it.

As for the flight conditions (IMC/VMC) and rules (IFR/VFR), I'm not sure what you're asking. Is either pilot IFR current? If not, then the flight can only be VFR. This question might be relevant.