The Mormons sponsor units that comprise about 13% of the BSA's membership, as do the United Methodists. The Roman Catholic Church is about a percentage point behind them. Neither the Mormons nor the RCC are eager to see openly homosexual leaders, and I doubt the Methodists are either. The Mormons (who have been active in sponsoring Scout units since 1916) and the RCC would very possibly take a walk out of the BSA if it changed its policies in this matter.
I was a member of a troop sponsored by a Methodist church in Springfield, VA. Our troop members included a wide variety of protestant denominations, Catholic and Jewish. The scout summer camp provided services for each and every faith present at the camp.