Oracle query against SQL Server database giving inconsistent results
I'd suspect some for of characterset conversion issue.
When you do a TO_CHAR, you are getting back "┐┐┐┐┐┐┐┐┐┐┐┐┐┐┐┐┐┐" (18 characters). That suggests that there is some confusion about whether the data contained in the column is single-byte or multi-byte.

"The uniqueidentifier data type in SQL Server is stored natively as a 16-byte binary value"
This should ideally come across to Oracle as a RAW datatype not a VARCHAR2 or CHAR.

If you do a 

CREATE VIEW temp_view as select  "id", "folder_id" from dbo.mediasite_presentation@ms


what shows up when you do a DESC temp_view