AWS does not consider FCAW and GMAW to be the same process. I am referring to paragraph 4.1.2 of D1.1 (2004) (my 2006 edition is in the van). The paragraph lists the welding processes and it separates GMAW from FCAW.
Since FCAW is not used to weld aluminum, I wouldn't expect to see it listed as a welding process in D1.2.
So, where I would agree with Lawrence with regards to the use of GMAW within the previous six months, I would further say that he would have had to use the spray mode transfer inorder to keep his certifications valid. I say, "use the spray mode" because AWS D1.1 considers short circuiting to be separate process from spray or globular.
I would agree that provided the welder has been qualifed on both carbon steel and aluminum using GMAW spray mode transfer, the certifications would be valid as long as continuity for the process can be verified.
Good luck - Al