I'm playing a league based on a 1986 Lahman import. I've got it set to import real rookies and I set the first draft for June 15 of '86.
I just ran the draft, and many of the "real" players who were chosen came into the league with 3-4 years of Pro service, making them immediately eligible for the Rule 5 Draft.
Take, for example, Jeff Treadway
Just drafted on June 15, 2006 - the current day
He's already got 4 years of "time as a Professional", making him Rule 5 Eligible unless I put him on the 40 man roster.
This effectively kills the Rule 5 draft for this league, and probably for most leagues using real rookies.