Also Xanadu Blood has strong synergy with it, while also infcliting it left and right.
XB has zero synergy with breach unless brought in as a reinforcement. You might argue that its synergy is "strong" if it is used as a reinforcement, but I wouldn't go that far. It increases damage against Breached enemies & breached enemies inflict less damage. That's useful, sure, but but a flat +%Offense & +%defense would be more useful, since it would apply universally and would not allow the enemy a chance to resist.
Basically, yes, XB has synergy, only when used as a reinforcement, otherwise zero synergy, and the synergy that exists isn't impressive.
HT has some but not great synergy with Breach at first glance, but because it's the best tank in the game, because the particular form the synergy takes is to keep HT taunting, and because on basic it heals itself if it has taunt (and it gets/maintains Taunt because of Breach), it has that extra bit of synergy with Taunt that is effectively a back-door synergy with Breach.
Literally every single ability (except the reinforcement) on IG-2000 has synergy with breach.
Finally, I agree that IG-2000 has the strongest breach synergy, but IG-88 is a toon on the low-end of mediocre, so to get that ship working at useful levels you have to gear a toon that I would never bother to gear otherwise. Without a high-gear IG-88 you might have tight Breach synergy, but you have tight synergy on a worthless ship. I don't remember if IG-88 requires any StunGuns (though I doubt it requires many, as an attacker), but I wouldn't want to give him any of those in today's game. My IG-88 is g10, but that was done long, long ago & I haven't touched his gear or his mods in maybe 3 years.