User blog comment:B214/Question and Answers 6/@comment-180.253.126.123-20160717091644/@comment-26345952-20160717144942

Yes, Issei was wearing his Scale Mail in the spar with Millicas at that time, but around the time with the incident of the rough magicians balance breaker could not be an option (seems like Ddraig condition was a bit worse or his consiousness was further away). Issei could dragonify himself as it was a power from his new body.

Out of all the Super Devils we have only seen one who has a true form, Sirzechs. Rizevim does not, and although he is known as a Super Devil, he is the weakest of the three. Ajuka is a mystery, we know that his power and strengh is at least the same as Sirzechs, but weather he has a true form or not is something I dont know.