*Most* outboard housings are just that, a housing. The only thing spinning in there is the driveshaft, everything else is covered. IF any remnant's made it down to the lower unit, they would just lay there till it's serviced next time.
However, IF the threaded part of the zerk went in to the section that gets the grease, it could damage a bushing or bearing.
Was it a threaded zerk, or a pressed in type? I've seen the pressed in ones just pop out before.