Helen S. Wright’s 1988 A Matter of Oaths is a standalone (thus far) space opera.
Desperate for crew but short on qualified candidates, Commander Rallya of the patrolship Bhattya grudgingly hires Rafe. His service record is glowing, his professional qualifications are exemplary, but … Rafe has been mind-wiped, for reasons about which Rallya can only speculate.
Not having a choice really speeds up the decision making process. At least Commander Rallya can be sure that whatever Rafe’s past, identity erasure has made it completely irrelevant to his present.