It should work, yes (and folks have reported it working before):
For a test Machine app I run, I see it work:
fly dig AAAA _api.internal -a <app-name>
;; opcode: QUERY, status: NOERROR, id: 35964
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; ANSWER SECTION:
_api.internal. 5 IN AAAA fdaa:0:<orgid>::3
Are you querying for AAAA records? Some are TXT records too (ref docs).