By the way - I might have noticed this sooner had I not been so pleased with the success of this method from the player perspective - but AI ships remain invisible, as it turns out.
I've tried two or three things to correct this.
1) I created templates and ships with the names of the default ships (like HvyFighter, Frigate, etc.) for the Borg Style and saved them appropriately.
2) I changed the AI templates in the Borg Style.xml to those specific templates created for the Borg.
3) I tried #2 again, this time making sure that the templates used the same hull size as the default "Attacker," "Defender," etc. AI templates used, thinking that might have been what was at issue.
None of those attempts fixed the problem. When playing against the Borg custom race I created, AI ships (such as "Borg Scout" and "Borg Fighter M6-02" or something to that effect) are consistently invisible. There are templates for all the hull types and sizes, so I can't figure out why this is occurring.
Playing as them still works fine, though.
Any thoughts or suggestions? You have my continued thanks!