Hi Brandon,
I must strongly disagree about Vadi being compatible with any German longsword source I have seen.
The following are observations based on a reasonable knowledge of Ringeck and only a few readings of Vadi so I could well be wrong.
However::D
As far as I can see.......
Vadi's wards are very much on the centreline and do not seem to create binds at the same angle as occurrs in Ringeck. Because Vadi's cuts are "pushed down the centreline" rather than chambered from above as in Ringeck, the bind in my experience tends to be realised with the swords alot more upright in Vadi than Ringeck.
A REALLY big difference is that Vadi often tells us to use double time defences. In doing this he tells us to move into the blow and choke it up which is the opposite method to most people's interpretation of Ringeck.
This is my current theory as to why winden are not used by Vadi: With the swords closer to vertical, a volta (similar to a German twitch) makes alot more sense than trying to wind against a sword that could easily disengage from your bind due to it's lack of lateral commitment.
Another important difference is that Vadi uses (and even writes about) a very linear stance. Ringeck (for me) seems to work best from one that is quite broad by comparison.
Vadi also has that very cool false edge circular parry method of dealing with mandritti which interestingly in found in later Italian single sword manuals. Although you wouldn't use this parry all the time, it does create a different feel to the fight. (I LOVE this parry)
I really don't think mixing these methods is a good idea.
Cheers,
Stu.