do you mean Direct Attach Cable?
I tested it with HP SFP+ DAC Cable and the connection worked fine.
Only the picture of the firewall in smc is not correctly displayed.
Please see my Question "Wrong interface type".
That's right, is DAC but cisco call it Twinax.
Regarding your issue, did you use DAC at both nodes or only in the one that reported the interface as RADIO?.
yes, i used the DAC only in one node.