You should not issue shutdown commands from instance on Solaris Cluster.
The clusterware will see this as failed resource group and will failover on another node.
What you need to do is :
Identify the cluster group resource which is responsible for resources.
clrg show and
clrs show will tell you that.
After you have identifed the cluster group(s) responsible for database you will just need to do a
clrg offline group-name
This will stop everything related to database (every resource in resource group[s]), umount filesystems if used, stop ASM etc. -> depending on the resources configuration and database resources setup).
If you want to tinkle around the database while resource group is online you will need to put its resources in unmonitor state
clrg unmonitor group-name .
Be sure to return them to monitor after you are done, or risk failover not happening.
Test this on virtualbox cluster or test enviroment, setup a small cluster and get into resource groups and resources
I haven't done this with oracle databases, but i have with NFS and HA filesystem on sun cluster.
Hope that helps.
Regards
Peasant.