Ethan, I believe pressure bleeding is recommended over vacuum bleeding for ABS systems for the very problem I mentioned. During vacuum bleeding, there is a danger that a small bit of air that gets sucked past the threads can remain in the caliper. This bit of air can cause problems with the ABS system. I believe manufacturers actually warn against using vacuum bleeding. Otherwise I don't see a big difference between pressure bleeding and manual pumping in ABS systems.
The suction device I use is home-made and resembles a hookah. I use suction with my mouth to produce the vacuum. I find it useful for other jobs such as removing brake fluid from the master cylinder or fluid from the power steering fluid reservoir. Without the vacuum, it works well as a collection jar for bleeding the brakes.
I think air gets past the threads regardless of the vacuum source.
95 E320 Cabriolet, 131K