Do vendors ever have any information to share?
No they do not, all they do is complain about the settlement or grumble about something or the other (in all my playthroughs, and siding with different factions). Once in a while they may talk about something you have done/a nest you have cleaned, etc. But that's about it. You can learn about new missions/places/enemies from other NPC's though (mostly from eavesdropping in the big cities for example or creeping up on Raiders/Gunners and listening in).