"In prison? By that, do you mean Horen Gertrude?" The lead Sorcerer asked, a bit perplexed as to why Vhelian brought him up.
More likely than not, a Rahichna Sorcerer would hide the true nature of their capabilities. Some might even hide the fact that they were in possession of a Rahichna.
As for Horen Gertrude, it was announced during his ascension as the heir to the Dukedom that he had a Rahichna. However, he didn't disclose what he was capable of.
Truth be told, even if Horen had a Rahichna, the Obelisk wouldn't take interest in him.
First, he was the heir to a Dukedom, hence it would be difficult to make him leave his role just to be under the orders of the Obelisk.
Second, he wasn't in their radar by virtue of his lack of efficiency in wielding Manna. He failed one of the tests conducted by the Obelisk. In that test, the Obelisk examined the capabilities of an individual as a Sorcerer.