I haven't finished installing 10g yet, but from what I know about UNIX, I'm not sure why ASSM would be looking for device address drivers found in /dev. The /dev directories are used by the OS to map logical to physical (you have directories like /dev/dsk and /dev/rdsk - those come into play when installing the OS and formatting). I would think that Oracle would be looking for mount points - the human readable names - for file systems, such as /opt, /opt1, /u01, whatever - but definitely NOT something in the /dev/whatever realm.
You may have the disks on your file system, but how do you reference them by partition name (e.g., df -k)? For Oracle going to the logical/character DAD names in /dev would be something new.
I see the disks now. The sysadmin had to map /dev/sda to /dev/raw1, etc. first. Strange.
I'm running root.sh now and it's complaining about CSS and CRS (something to do with clustering). It's saying that ASM cannot be used until Oracle CSS service is started. I logged a TAR and I'll update this if I actually get it running.