I can imagine a few problems that might arise but these players have already played two campaigns there and it's not too canon heavy anyway. And I have a couple of character ideas I want to use.
D&D Home Page - What Class Are You? - Build A Character - D&D Compendium
Here's my experience with multiple DMs in a single world. (If you haven't already figured it out in the past 2 weeks) I have DM'd two separate campaigns in my friend's world. The most important things to take care of were:
1. Where on the world is the campaign taking place?
2. What time period does it take place in?
3. Are current conflicts and politics connected or separate in the two campaigns?
And also handling NPCs/Enemies and how they relate basically. Hope this helped.
I've played in settings where all DM's used the same world. They basically redefined the map constantly, and the players just moved to new unexplored areas of the map. But over time it became very important to keep a logbook of all the cities and rulers, with descriptions of what they looked like. This way we could keep the world coherent when revisiting old locations. I often found great joy in reusing npc's from the campaigns of other DM's, and to have not just reoccurring characters, but also reoccurring locations. Of course every campaign was it's own independent story, so there never really were any big continuity issues. On occasion we've redconned the death of a fun npc in someone elses campaign, sometimes by involving timetravel. But it is a lot of fun to be creating the world together.
Sounds like fun, so long as DM's keep open communication between each other