And I don't think that this is the point: Through my discussions with German members of the KSR I learned, that the decision of not allowing aikidoka to enter the ryu has very deep contentual reasons. They truely think that someone who practices aikido has made decisions - in his mind and his body - which don't allow him to use body and mind to do what has to be done or to think was has to be thought when doing KSR.
I don't buy it. It seems much more likely that the lion's share of unsuitable candidates their instructor gets knocking on his door are Aikidoka and want to train in the source of Tissier's sword, so he's come up with a blanket excuse for a default "no."
I could see requiring new students to drop all other arts entirely because you have to start with a clean slate, or even requiring that new students have an established skill-set of some kind or else they are required to cross-train in something specific.
Given how diverse Aikido styles are in their training and emphasis, it really seems like there is something else going on if the prohibition is particularly against Aikidoka.