Is it permissible to log an instrument approach for purposes of IFR currency in a non-IFR certified aircraft? Assume you maintain VFR at all times and you have a qualified safety pilot on board. Can an IFR rated pilot fly practice approaches under the hood (view-limiting device) using an aircraft that is not IFR certified, and log these approaches for purposes of meeting his/her IFR currency?

Assume the aircraft has the required equipment for the approach (i.e. VOR for VOR approach, ILS for ILS, etc.).
As long as you remain VFR then the equipment requirements for the airplane and the flight are VFR. 

§61.57 says “Within the 6 calendar months preceding the month of the flight, that person performed and logged at least the following tasks and iterations in an airplane, powered-lift, helicopter, or airship, as appropriate, for the instrument rating privileges to be maintained in actual weather conditions, or under simulated conditions using a view-limiting device…”. 

It doesn’t say anything about having an IFR certified airplane or having a current pitot/static and altimeter check. If you are maintaining SEL IFR currency, then all you need is a SEL airplane. MEL IFR, then a multi-engine plane, etc. And if you are missing some of the 6-pack instruments, all the better for practicing partial panel.