Edit:
If one player has turned of experience earning in options, they will not earn experience for the pact. However, the experience earned by their partner will go into a "bank" of sorts, and will be awarded when the player turns experience earning back on, bringing the character up to their partner's experience level.
Source : wiki
(Seriously. Bookmark the wiki. I've gotten to where I go there before asking things. Quite often it's there.)
Right, I didn't think about checking the wiki.
Thanks. 
What would happen if one member of a leveling pact turned XP earning off? Would the other person gain full XP?