I THINK I FIGURED IT OUT!
JaoSming, could your awesome NBA LIVE 08 knowledge tell me if this makes sense....
this will work if i create a teamcode of NBA Team (0) BUT give them a conference of something other than West or East (such as 2 = all-stars + brand teams, 3 = ref, 4 = decade all-star)
why it will work:
NBA Team code (0) shows up in play now (play now can work with over 15 players because anyone about spot 12 is IR and does not show up during gameplay), practice, player edit, roster reorder, SIGN/RELEASE, etc.
Since Dynasty is only for NBA Teams (0) that are in the East or West conference (0 or 1)...then they will not show up in dynasty (unless u select them at the beginning....

)...thus no crashes for an over 15 player team in dynasty
does this make sense!?
only thing i need to test: what if dynasty season schedule is selected as Random and not NBA...will the game create a new season with this "NBA non-Conference" team?