I was pleased to find that I could call structs that I had set up in vb.net straight into excel vba - using COM visible and registering using regasm.exe.
I am strugglin
Hans Passant's solutions in the comments above perfectly solved the problem:
In VB.net, either use:
Public Function ReturnDict() As System.Collections.IDictionary
or reference scrrun.dll and:
Public Function ReturnDict() As Scripting.Dictionary
Dim dict As New Scripting.Dictionary
The latter solution provides a VBA dictionary that can be used as one would like.