I am not too familiar with the Storage Viewer for vSphere Client - however, the manual says for discovery of CLARiiON arrays, an user name and password is needed on the array - and it seems to me that any user with "Monitor" role will be sufficient for this, since you are not going to do any administrative tasks or configuration changes on the CLARiiON from Storage Viewer. However, I understand, using a user with "Administrator" or "Manager" will not cause any harm - it will be upto your decision.
My 2 cents
Yesterday I actually implemented Storage Viewer using a CLARiiON user with "monitor"
privileges. So far everything appears to work. The reason I am limiting the privileges is
for security, to minimize the amount of accounts with write access. If there is no reason
for this account to have write control, then it shouldn't have it.
If I find a reason for the Storage Viewer CLARiiON user to have write access, I'll update
there might be in the future. For example the new Storage Viewer for Celerra allows you to create snapshot, create file systems ..etc, so for that type of access you would need account with elevated privileges. Soon VMware admins will not need storage guys ..they can take of everything themselves (that's a scary thought)