I think that Demandred's statement in tGS, that he would have claimed Semirhage's life if she killed Rand in his stead, proves that he has never sent henchmen to kill Rand. He wants to do that himself.

So I think we can undoubtedly say he didn't send Rochaid and Kisman, and he isn't Slayer's patron either.

In my view, both of those commands were given by Arangar.

But I do not think this discounts Demandred as being involved with the Black Tower. We know he had to be the one behind Taim, since Moridin was still dead at this time.

So Demandred used Taim as a proxy, and Kisman and Rochaid and the gang as well, to take over the Black Tower. I just think that Demandred didn't get his hands dirty here, and therefore didn't spend time mixing with the common Ashaman like Flinn.

That still doesn't preclude Demandred from pulling the strings on Taim and his henchmen from afar.

Evidence of this, in my mind, is Taim's unhappiness when Rand picked Dashiva to accompany him. Dashiva is Moridin's man at the Black Tower, while Taim reports to Demandred.

Hence Taim's unhappiness that Dashiva - over whom he has no influence - gets to accompany Rand everywhere.