I found a blog post that mentions a similar issue and MOS note that references the issue and workaround solution:
ASMLib: oracleasm createdisk command fails: Device '/dev/emcpowera1 is not a partition [Failed] (Doc ID 469163.1)
Now while this references EMC storage, the same issue and solution applies to other multipathing software and storage arrays such as Hitachi storage with HDLM in my case.
Instead of using the 'oracleasm createdisk' command I had to use an internal tool called asmtool that usually is called behind the scenes by Oracle tools.
# /usr/sbin/asmtool -C -l /dev/oracleasm -n VOL1 -s /dev/emcpowera1 -a force=yes
This saved me hours of frustration this week when I had to build new ASM disks and do a migration for a customer solution in a very short time period. Hopefully it will also save you hours of grief .
Getting used to Hitachi storage is a bit new for me but since I have years of EMC storage administration experience it is not too steep a learning curve and quite a bit of fun learning new things!