You can use ISCSI disk slice for metadb.
Or any disk device slice as far as metadb is concerned.

With metadb command (not metainit), you use defined small slices on disks, not the entire devices (cNtNd0 or cNtNd0s2).

After metadb creation, you may use SVM via meta commands for managing metadevices and metasets.

Just be sure that those luns will be present on machine as long as SVM is used.
Or, if old luns are removed, and new one added, add new and put extra database replica on it.

Remove replica from from old LUN, then remove the lun from system.

Having one metadb slice on one disk is a bad idea anyway.
You would want at least two, spanning on multiple disks (not same disk multiple slices).

Only place in which you can or must use entire devices (cNtNd0s2) is
Copying partition table from from same sized devices prtvtoc .. | fmthard ..
Using dd.
Creating zpools.
SCSI,multipath, zfs debug, information and manipulation using luxadm, mpathadm and zdb commands.
Others i cannot remember now.

Good thing to mention is that using the whole disk during zpool creation will enable you to import that zpool on x86 or SPARC architecture due to filesystem endian awareness.

This, of course, provides data moving from one platform to another, not binaries.

Hope that helps
Regards
Peasant.