So, I tried to eke Summon Bats or some other weirdness out of the twitching bat wing or the giant bat wing.
-Killed both Bat Swarms and Flying Eyes multiple times with Etheric (and Ranged) Techs while Etheric.
-Got 20+ etheric.
-Ate a marshmallow bat.
-Ate a crisped Bat wing.
-Took a castor capsule and vomited out stuff.
I did all of these things twice. Once with the twitching bat wing equipped, once with the giant bat wing equipped. Absolutely nada, so I feel fairly safe in saying that Summon Bats either isn't available or is buried rather deep.
Also out of curiosity, I also had Writhing Flesh active and the fully Ratty Suit Disguise when I ate the crisped bat wings. Obviously nothing came of those too.
Writing for the long-neglected GOC Casefiles canon.