Looks like you're right. I don't have an Oracle DB to test, but I just played around with it on a MySQL DB, and invoking 'SHOW' this way works fine:

perl -MData::Dumper -MDBI -we'$x=DBI->connect("dbi:mysql:wp", "yeah", 
+"fer_sure"); print Dumper($x->selectall_arrayref("SHOW VARIABLES"))'
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-- 
I hate storms, but calms undermine my spirits.
 -- Bernard Moitessier, "The Long Way"