You can test the table .Uniform property before processing and either skip the table or process it in a different way if it's false. For example:
Code:
Dim Tbl As Table
For Each Tbl In ActiveDocument.Tables
With Tbl
If .Uniform = True Then
'Process Uniform table here
Else
'Process non-Uniform table here (or skip it by leaving out the 'Else' statement)
End If
End With
Next
Note: The .Uniform property tests for merged cells - horizontal and vertical - as well as cells of varying widths in a column. It returns False if any of those conditions exists.