Add-ins are, in theory, independent. The only way I can see a conflict occurring is if two add-in authors chose the same name for a DLL or other component that's part of their add-in, or if two add-ins install incompatible versions of the same helper tools, e.g. different versions of a database.
In any case, for just about all such problems you'll have to try it and see. I've never seen any reports of sequence issues, for what that's worth.
I'm not on the WHS team, I just post a lot. :)