Camarilla
Let's say, you are an open Camarilla member actually sent by Sabbat. The odds are very high that you are Blood Bound to someone, maybe mutually, maybe not (after all, that's what Camarilla is infamous for). This will make it a hard decision to give info to Camarilla enemies. After all, you understand that it may get killed those who you are bound to. If bound to noone, that may look very suspicious. I can imagine such a character being a spy, but not really for long, he would get caught in a single chapter, and recruiting more spies would be very hard because of that.
I thought about participating in Vaulderie as a possible way to fight the Blood Bond, but it is a risky practice. If a spy cell is present, it may be easier to hide the Vaulderie, but if one cell member is caught…
And not even mentioning having to go outside to take Vaulderie, it's suicidal.
Sabbat
Now let's say that you are with Sabbat officially, but try to spy for the Camarilla. You have to participate in Vaulderie frequently, which ruins any existing Blood Bonds, and makes you interconnected with more and more Sabbat members. Once in a while, you will simply be unable to take any actions against the Sabbat, at least the part you are infiltrating, and are likely to become a real Sabbat member. If you don't participate in a Vaulderie and actively avoid it, you will live a very short and unhappy unlife.
Both sects
Of course, Madness Network or SchreckNet could do the job, but they are both limited and as far as I know info gained this way is normally not fully shared with the Sect.
So, what am I asking about:
- Canon examples of spies (and by "spy" I actually mean a mole or a sleeper agent) from any canon books, which also tell how did they fight supernatural ways to control them (Blood Bond, Vinculum).
- Mechanics that would allow to avoid mentioned restrictions and be a successful spy.
I am not interested in a complete list, it would be too big, though the more examples I get, the clearer things become.
Best Answer
Clearly any techniques of spy craft will work on any vampires in the same way they work on humans: ideology, shame, revenge, and greed pretty much cover it all. These techniques are out of scope but you can be found easily. there are literally hundreds of such methods used everyday in real life.
One of the most common might be the "enemy of my enemy is my friend": So, group A and B are both Sabbat and both hate each other. Prince Y of the Camarilla contacts A and seeks a temporary alliance to mess B up. What could go wrong⸮…
Vampire have access to mystical powers: Dominate and Presence, used both in conjuncture, can achieve complete control over a person in such a way that the person does not remember being controlled. Thus, a vampire could condition another to write a journal of what they are doing. A repository of what they feel, what they do, who their friends are, and hopes for the future. The writer then sends a copy to their master and forget they did so. A perfect spy who does not even know they are a spy.
Note that RAW does not quiet support this: You can make it work but it is akin to putting a round peg in an oval hole. In my view, disciplines were always more than discreet powers and their use could be morphed with enough mastery and training. Your mileage might vary.
With this in mind, a sleeper personality might be implanted in a young vampire, ready to take over on the right trigger a la Manchurian Candidate.
To answer the first part, I am not aware of any sleeper in either sects within the published material. However, it's been years since I read them so could not be remembering.
And because a good conspiracy theory is always welcome: You know that the Sabbat and the Camarilla were created by the Elders as tools to distract the younger vampires from finding out they are just food? Thus it is entirely possible that the Vaulderie is not as efficient at breaking blood bounds than is believed… Some elders within each organisation have a good knowledge of what is happening in the other.