To some extent they're interchangeable, but I think there's a slight difference in implication. If I say:
Jimme would be proud of you (if he knew/could see this).
it can imply that Jimmy potentially had the opportunity to see the event but didn't due to some 'temporary' event (not finding out yet, not being there at that particular moment). Whereas:
Jimmie would have been proud of you (had he still been alive/living here).
has slightly more of an implication that it was not possible for Jimmie to witness the event due to some fairly 'definiitive' previous event, e.g. dying, moving away etc.
However, these are implications rather than hard-and-fast differences in meaning. To some extent, they are interchangeable with either meaning.