The last book kind of answered the question about magic and the LV virus. While Declan was healing with the infused LV virus from Senka and Chris he could not draw outside energy into himself because it would realign his cells back to magic usage versus the healing benefit provided by his cells being realigned by their LV additions. So if a witch can be turned most likely they would lose some if not all the cell alignment needed to use magic effectively. So maybe a were or vampire with limited magic could be the result. The demon-were hybrid could do magic, but used very little of it from what I read.