Resolution:
A customer raised the question whether that was just for installation,
or whether the icadmin needed to be permanently part of the dba group.

The general recommendation is to keep icadmin permanently
part of the dba group.  It is definitely necessary to have
icadmin be part of that group during installations and upgrades.  This is because
the installation and upgrade create both tablespaces and removes and update the structure of
TIBCO InConcert tables.

During regular operation, the icadmin user needs to be able
to update database objects owned by database user
icdbown.  It may be possible to take icadmin out of the dba
group during regular operations, and restore membership when
system-level changes are required.  The general recommendation
is still, however, to keep icadmin part of the dba group
permanently.