In our league play a two man umpiring crew got caught out of position. The play involved a third out made at third base when the batter tried to turn a double it a triple and if the lead runner from first base had crossed the scoring line. Both umpires did not see if the lead runner had scored and the PU asked the scorekeeper who was sitting right behind home plate what he saw. The scorekeeper advised the runner had not reached the scoring line and the PU ruled no run on the play. The aggrieved team protested the use of the scorekeeper to assist in making the call. Can an umpire ask an off field official for help with a call? And is there a specific rule prohibiting this practice?
Thanks for any help in advance!

Nope.