Yes backups without wildcards work. Since my first post, I have discovered an interface quirk in how you input the Path.
I found that after clicking the "Advanced..." button. You can't just type in the path "\\mylinuxhost\/usr/opt/oracle/admin/*/exp". and press Ok. If you do so, you will get a backslash at the end instead of the normal Linux forwardslash. You can verify this by clicking the Text view and see your selection as "\\mylinuxhost\/usr/opt/oracle/admin/*/exp\*.*" I believe it is the backslash that was causing the e000848c error.
Instead you must at least navigate graphically through Remote Selections/Unix Agents/mylinuxhost/. When you click on , a slash will appear in the Path box. From there, you can type /usr/opt/oracle/admin/*/exp and press Ok. Now, the text view will show a proper selection with a forward slash just before the *.*, i.e., "\\mylinuxhost\/usr/opt/oracle/admin/*/exp/*.*".
I thought this would resolve the problem. The backup ends "successfully" but when you check the log it has not backed up anything but the directories up to and including admin. When I check the media the job used via a restore selection, the selection tree stops at admin and there are no actual files to restore.