Why would you need an XCP fee to put data in a Bitcoin transaction?
OK, my question was not as precise as your answer.

So, a BTC fee is required?
Yes.
... and
https://github.com/PhantomPhreak/Counterparty/, and Read the Docs.
The --fee_provided=.001 or --fee_required=.001 might be in XCP.
From what I understand, they are optional.
But honestly I don't know about them.
Not digged that yet.
Those fees are in BTC. See also
./counterpartyd.py order --help.