↓で動いた。

①ActiveXDLLなプロジェクトのClassで
Public Type UserInfo
　Id As Integer
　UserName As String
End Type

②標準EXEなプロジェクトで①のDLLを参照設定して
Sub main()
　Dim c As Collection
　Dim u1 As UserInfo
　Dim u2 As UserInfo
　Dim v As Variant
　Set c = New Collection
　u1.Id = 1
　u1.UserName = "Hoge"
　u2.Id = 2
　u2.UserName = "Fuga"
　c.Add u1
　c.Add u2
　For Each v In c
　　u1 = v
　　Debug.Print u1.Id, u1.UserName
　Next
End Sub