Для этого не обязательно создавать регион,
можно просто объединить линии и арки в полилинию,
потом ее заштриховать, к примеру:
Option Explicit
Sub JoinArcsAndLines()
Dim oSsets As AcadSelectionSets
Dim oSset As AcadSelectionSet
Dim fType(0) As Integer
Dim fData(0) As Variant
Dim varPt As Variant
Dim oLine As AcadEntity
Dim oEnt As AcadEntity
Dim commStr As String
Dim intPt As Variant
On Error GoTo Error_Trapp
Set oSsets = ThisDrawing.SelectionSets
fType(0) = 0: fData(0) = "LINE,ARC"
For Each oSset In oSsets
If oSset.Name = "LineSet" Then
oSset.Delete
End If
Next
Set oSset = oSsets.Add("LineSset")
oSset.SelectOnScreen fType, fData
ThisDrawing.SetVariable "PEDITACCEPT", 1
commStr = "_PEDIT _M"
For Each oLine In oSset
commStr = commStr & " (handent " & Chr(34) & oLine.Handle & Chr(34) & ")"
Next oLine
commStr = commStr & vbCr & " j 0.0000 " & vbCr
ThisDrawing.SendCommand commStr
SendKeys "{ESC}"
oSset.Delete
Set oSset = Nothing
Error_Trapp:
MsgBox Err.Number & Err.Description
End Sub
Дальше смотри пример из Help файла