Stranger,
Sorry for the late response. I haven't checked in here at KFO in quite a while and just happened to stumble on your post. I make somewhat of a specialty out of applying Baguazhang to bladed weapons combat.
RE: "How do Bagua's techniques with the knife compare to those of South-East Asian martial arts (ie. kali, silat, escrima, kuntao, etc.)?" IME, there simply aren't any 'Bagua knife techniques', per se. Therefore, a direct side-by-side comparison of specific techniques with those of SE Asian arts would not be possible. However, application of Baguazhang principles and movements to a blade does indeed yield an extremely effective method of combat. To answer the spirit of your question, though, I'd have to say that, done right, it can compare quite favorably.
As you mentioned, I also have a background in FMA, so I am able to make comparisons based on years of personal experience with both traditions. My experience, both for weapons AND empty hand combat, is that Baguazhang and Kali complement one another extremely well, strange as that might seem on the surface. IMO, the efficiency, brutality, and no-nonsense approach to combat that SE Asian arts generally exhibit combine well with the fluidity, whole-body power generation, sensitivity, etc. of Baguazhang. As such, it isn't always necessary to view such a comparison as either/or.
In the interests of intellectual honesty, however, I would point out that you are far less likely to find someone who truly knows what they are doing with a knife coming from a Baguazhang perspective than you are to find such a person coming from a SE Asian arts background. That isn't a criticism of Baguazhang's material so much as a result of the fact that bladed combat is part and parcel of SE Asian arts from day one. With Baguazhang, on the other hand, you aren't likely to find many folks who have a lot of depth of experience, skill, and/or knowledge of real-world bladed combat. It's just not where the emphasis is placed in the training. In fact, to my knowledge at this point in time, no other teacher in the United States does anywhere near the level of specific knife work in Baguazhang that I do, and most touch on it rarely if at all.
If you are looking for other alternatives beside Baguazhang or SE Asian martial arts for blade work, I might also suggest you look into Western European dagger styles, the knife material of Systema, John Perkins's Attack Proof material, and even various Native American approaches. And of course there's always Tanto-Jutsu and other related skills from Japanese arts.
I hope this has helped. If you have further questions about a Bagua approach to blade work, feel free to email me.
"Bagua can look pretty, especially when you wave your hands around alot and walk really fast and bounce back and forth like a goof." -- Braden