The view you're looking at is a built-in, read-only view. However it should not give you that error message (I'm getting the same error message, by the way).
The error is basically saying that "Bytes_Sent" is a non-indexed Custom Type field. Bytes_Sent is read-only, you can't enable indexing, unless you crate your own custom types field with indexing enabled. You will then need to update your parser to change bytes sent field to the newly created custom field.
I'd open a ticket with McAfee Support in this case because you should at least be able to view the configuration of the view w/o the error.
For the second part of your question, the unit measurement is set in both McAfee Web Gateway and SIEM in bytes, I can't tell you now w/o testing if that settings can be changed to anything other than bytes.