Approaches logged for meeting the recency of experience requirements of FAR 61.57(c) must be performed under actual instrument conditions, simulated instrument conditions, or in a simulator of approved flight training device. Simulated conditions means conditions which simulate instrument flight, and must at a minimum require flight by reference to instruments without outside aid. This may be a mechanic view limiting device, the brim of a ball cap, a full hood over the cockpit area, or a hand held over the eyes; something that simulates instrument conditions.
A safety pilot is required during simulated instrument flight, by FAR 91.109(b)(1). This pilot must posses at a minimum a private pilot certificate, with category and class ratings appropriate to the aircraft being used.
The safety pilot need not act as pilot in command, however, is a required crew member. FAR 61.3(a) requires that a required crewmember have physical possession of a valid pilot certificate for the privileges being exercised. 61.3(c) requires that a required crewmember have a valid medical certificate in their physical possession.
A safety pilot who is not acting as pilot-in-command need not be current for landings (day or night), flight review requirements of FAR 61.56, or instrument experience.
Note that a safety pilot is only entitled to log pilot-in-command time under specific conditions. The safety pilot must be designated the acting pilot-in-command, and in such a case must be current and capable of acting as PIC.