In the Major League part of the draft, a team must keep the player on the Major League roster all year, or if the player is injured and spends time on the DL, they have to spend at least 90 days on the active roster (which, if they're on the DL for long enough, could extend into the next year). Plenty of non-competing teams will draft prospects, stash them on their active rosters for 90 days, then find a way to call them injured and send them down for the rest of the year on long "rehab" assignments (we did it with Wei-Chung Wang, I think the Padres did something similar with Miguel Diaz). The minor league portion is more lax on both ends. There are minor league rosters that players must be placed on to be protected, and you can protect players at the AAA/AA level and so on down. So basically only prospects you've barely heard of are unprotected in the minor league portions of the draft with very few exceptions, and it's not really worth worrying that much about, since we won't lose anybody in that part of the draft that is really worth caring much about. I'd say once a rule 5 draft pick makes it through spring and actually gets on a team's active roster, the chances of that player being returned to the original team go down substantially. Although we have had players like Colin Walsh make the team only to fail pretty miserably and be sent back later. Long story short, it's possible that a player like Gatewood might not get drafted, but top 30 prospects would probably get drafted more often than not in the Rule 5 Draft.