I can imagine using dd to write over an existing file (since you can grab an extent map from ASM instance). But dd to _create_ a file inside an ASM disk group?...
once switched bring the db down and then use the dd command to copy the controlfile to ASM. We did this for a 4 tb database and were successfull.
-- Alexander Fatkulin -- //www.freelists.org/webpage/oracle-l