Of course, that's just the legal requirement. Never forget the difference between legal currency and actual proficiency. A pilot who hasn't flown instruments in more than six months might be able to stumble through the 6HIT's on a sim but still be a long way from being safe to launching off into the wild gray yonder.
If a pilot allows his/her instrument currency to expire, and you are within the ”second” 6 month grace period, can he/she become current again by using a simulator or can it only be done in a plane with safety pilot?
(14 CFR 61.57, 91.109)
A pilot is current for the first 6 months following his/her instrument checkride or proficiency check. If the pilot has not accomplished at least 6 approaches (including holding procedures, intercepting/tracking courses through the use of navigation systems) within this first 6 months, he/she is no longer legal to file and fly under IFR. To become legal again, the regulations allow a “grace period” (the second 6-month period), in which a pilot may get current by finding an “appropriately rated” safety pilot, and in simulated IFR conditions only, acquire the 6 approaches, etc. If the second 6-month period also passes without accomplishing the minimum, a pilot may reinstate his/her currency by accomplishing an instrument proficiency check given by an examiner, an authorized instructor, or an FAA-approved person to conduct instrument practical tests.