From 2003 to 2014, Dallas Cowboys vs. any team, in the regular season, play type is pass, play started in red zone, play featured Jason Witten[X]
http://tinyurl.com/qdr7y52
138 plays, 41 TDs, 53 1st Downs, 9 Interceptions, 1 fumble, Avg Yds gained 4.01
Rob Gronkowski
From 2010 to 2014, New England Patriots vs. any team, in the regular season, play type is pass, play started in red zone, play featured Rob Gronkowski[X]
http://tinyurl.com/p8mbk5m
84 plays, 41 TDs, 47 1st Downs, 3 INTs, 1 fumble, Avg Yds gained 6.42
Note 1st downs stat includes TDs
Other Misc stats (not Red Zone)
Targets per game Witten 7.0 Gronkowski 7.1
Receptions per game Witten 4.9 Gronkowski 4.7
Yds per Reception Witten 11.1 Gronkowski 14.3
Avg YAC Witten 4.0 Gronkowski 6.1
Witten has about 3 times as many games played so it's clear that the Cowboys don't go to him in the end zone as much as the Patriots go to Gronkowski. OTOH he hasn't been as effective in the red zone when they did, even though teams concentrate on Gronkowski more. (well, teams other than the Steelers do anyway)