I think it's very likely the 3rd player Seattle wanted was DGB. There was the rumor about Seattle looking to trade up early in the 2nd. In another thread, two people confirmed from watching the war room live feed that JS was sitting with three cards in front of him, until DGB was picked, at which point he picked up one of the cards, ripped it up, and threw it away. There were other rumors pointing DGB, and it just made perfect sense for Seattle in general.
I think DGB was to JS what Nelson Cruz was to Jack Z in 2014. Just because he went elsewhere didn't mean there wasn't immense interest here, or that there wouldn't be a 2nd chance to get him in the future.
Regarding Big WRs, Seattle did pick up Austin Hill in UDFA. Hill is 6'3", 212, and had a chance to be Michael Floyd 2.0 before his devastating knee injury in 2013. Hill played almost all of his snaps in the slot for a spread offense, but he runs good routes, is physical with strong hands, and high points very well. If he can recover and get back to being the guy he used to be, he could end up being better than some of the big WRs Seattle passed on at #63 and #69.
Smaller players tend to be extremely pass / fail. Look at Russell Wilson compared to all other short QBs who attempt to break into the NFL. 5'10", 190 pound WRs who dominate like Antonio Brown and TY Hilton are very rare. Lockett could be a star or he could be Deon Butler all over again.
My gut feel is that Lockett will do very good things on scramble drills and on double moves. Other than being size-redundant with some of the other WRs on our roster, Lockett's strengths seem to fit Seattle's offense perfectly. I think if he can make the leap to the NFL anywhere, it's in Seattle. And if he can be the same guy in the NFL that he was at K-State, he's one of the steals of the draft.