If I remember right, the trader has to be within a trader protected area to give quests. Not sure if that's a bug or what, but I do remember talk about traders doing this in other threads a while back.
There is a replacement (which I wrote) in 0-SCore called "RandomTaggedPOIGotoSDX". It is a drop-in replacement for "RandomPOIGoto", except:
you can optionally specify the POI tags ("Tags", not "QuestTags") to include and/or exclude;
it supports a "distance" property (either max distance, or "min-max" like in buried supply quests); and
most importantly for your purposes, it does not rely on a trader protection area to determine which prefabs to send the player.
Once you install SCore, you could use XPath to substitute "RandomTaggedPOIGotoSDX, SCore" for "RandomPOIGoto" in all vanilla quests. It should just work.
It is C# code, so it needs to be installed on both clients and servers, and EAC needs to be turned off. But if you really want to put quest-givers outside trader-protected areas, then I think this is your only option.