Any team will be able to draft any eligible player who was not added to the team’s 40-man roster. Most teams protect their top prospects, but every once in a while a star slips through the cracks. The most famous Rule 5 pick was Johan Santana.
Many people don’t realize that Marwin Gonzalez was a Rule 5 pick by the Red Sox from the Cubs before he was traded to the Astros. This is a way not to have prospects stall out in the farm system and give them a chance to play in the big leagues.