The Peddler 'synergy' seems to be that's Scout is a non-terminal. So it's the same kind of synergy Ruined Village has with Scout.
Not entirely, no. Scouts main synergy with any cantrip is that it increases you initial search space by 60% to find some enabling card. For instance. Say my enabling card for Peddler is Sir Martin and his lovely +2 buys (it could also be Market or Margrave). Without Scout, I'm looking to play Peddler and hope he is in one of the 5 cards in my final hand (or that I chain Peddlers to hit him), with Scout I'm hoping that he is in one of the 8 cards I see. Even better, I can stack my deck a bit so I can play Scout -> Peddler -> Peddler -> Martin this turn and CCXXX next turn. I am
much more likely to have a two or three peddler buying turn with Scout than nothing or most any other terminal $4; Silver is actively bad in a lot of these decks.
The problem is not that Scout is actively bad in a cantrip heavy deck, it is that you almost always want something else instead. For instance, instead of Sir Martin, say your activating card for Peddler is Squire, well in that case Scout competes directing with just buying another Sqr. Instead of trying to hit your 1 key card in 8, you are much better off trying one of your 2 key cards in 5. Roughly speaking, a second enabling card doubles your odds of lining things up, Scout is only competitive at lining things up if you expect to draw 3.5 cards or fewer (and if you are doing that you really want to make sure you have the attack as well). At some point, it is better to add Scouts than additional copies of a card (particularly if they are otherwise dead) ... but by that point you most often need to buying other things like VP, plats, or high end actions (e.g. Forge, Kc, Giant).
Scout's problem is the opportunity cost. When you want it, you want to buy something else first and Scout rarely has a good buying time except when you whiff on some price point or something else piles out.
