Can the 6 in. x 50 ft. Galvanized Steel Roll Valley Flashing be used for deck ledger and will it have chemical reaction with pressure treated lumber?

It can be used for deck flashing and it will not react with pressure treated wood.

Yes, the 6 in. x 50 ft. Galvanized Steel Roll Valley Flashing can be bent and used for deck flashing and it will not react with pressure treated wood.