I want to make a statement about the OP, because I haven't made a post in this thread before. Then I am going to make a separate post about the White Council though it will have to wait until tomorrow because I have a lot to say. I'll just tease that I have a totally different take on the Council's attitude towards Harry than I've read so far in this thread.
"Has Carlos sided with the Merlin against Harry?" Turn that idea around. Has the Arthur Langtry, A.K.A. the Merlin, attempted to recruit Carlos Ramirez to his point of view? We don't have any proof of this, but it makes a great deal of sense that Arthur would at least make the attempt to do so.
There is a description of two characters in the John Le Carre novel "Tinker, Taylor, Soldier Spy" that would seem to fit the Merlin and the late Warden Donald Morgan quite well. Together, these two characters were seen by their fellow members of British Intelligence as "the iron fist inside the iron glove." One of them was higher up in "The Circus" (MI6 I guess) and involved in planning intelligence operations while the other character was performing the actual field work. The one who got his hands dirty, so to speak. Arthur Langtry and Warden Morgan might have been described that way.
The Merlin probably feels the need to replace Morgan. Someone high up in the Wardens. Someone who can; to a degree, monitor the activities of one Harry Dresden. Though Morgan hadn't been able to do that after the events in Dead Beat. Harry mentioned Carlos reputation as a rising star within the Council, so that would appeal to the Merlin. Recruit someone the younger wardens like and can relate to.
Finally, after Carlos was nearly killed by Molly, it's possible the Merlin made an inquiry to discover what happened to the young warden. It wouldn't have been a personal secret that Carlos' physician; I think it was LTW, would have to keep from the Merlin. Arthur Langtry would have seen that incident as something he could use to sow doubt in Carlos' mind about Harry. Think of ideas, if not the exact sentences, the Merlin might have used to persuade Carlos. Molly was a warlock and she was Harry's apprentice. Harry trained her and now as the Winter lady Molly can't control herself. Do you think the Winter Knight can do any better when he is under the direct orders and influence of Mab? What about Harry's dalliance with the White Court? It isn't a one time event. He has been at Raith's mansion in Chicago several times and has made common cause with Raith's on several occasions. Harry Dresden needs to be protected from himself, before its too late.
I could go on, add more negative thoughts or give these ideas more detail, but I'm pretty sure everyone gets the point. I feel fairly confident Langtry has recruited; or has begun the process of recruiting, Carlos as his new right hand. However, there is one other factor that makes Carlos Ramirez the perfect target for the Merlin to recruit. He is young and naïve; relatively speaking, to the remaining "old guard" members of the wardens. Remember in Turn Coat, Harry asked Morgan if he knew that he would be blamed for La Fortier's death, that there wasn't a reasonable way for Morgan to defend himself. Morgan's reply was "I've seen it happen before." The remaining "old guard" has as well. More than that, they saw that the Merlin was ready to sacrifice Morgan to save his position and did sacrifice Morgan's memory and reputation in an attempt to make the White Council look strong. With that example, it is not likely many or any of them would want to take Morgan's place.