Clientside hit-detection for repair guns is a no go. That's A LOT of calls that need replication since the repair gun has damn near no fire rate, and isn't just the same as every other weapon in that it's a projectile or instant-hit weapon. It has it's own code to work through.
However, this is a moot point. By next week (if I can get in touch with server owners), bugged C4 should be a thing of the past. Already tested it, and yes C4 still floats if you throw it on a closed door then open it, but it is still disarmable since it updates its location for everyone after awhile of being thrown. You'll actively see mines sort of 'jerk' a bit after half a second of sitting or so.