This article is from the Progressive Music FAQ, by Phil Kime(Philip@kime.org.uk) with numerous contributions by others.
No, Jobson was not a member of Crimson, but he did get called in to
do overdubs on *USA*. Apparently Fripp had fired Cross by that point
and needed someone to do the overdubs. The majority of what you hear
on the album is Cross. Jobson did not perform the material live.