not sure what you meant about dragging something somewhere, but --
-- a widget in Aqua Mail always "points to" one of:
- A folder
- An account (all of its folders)
- The smart folder
What you can do is set up multiple "per-account" message counter widgets, maybe use "orange for work and purple for personal", that sort of thing. It would still be 1 widget per 1 account, not 1 widget per account group / type. Sorry.