What I recall from the e-budo thread... perhaps Chris Li can elaborate on:
Apparently Tsuruyama claimed at one point to have received a menkyo kaiden from Hisa Sensei, which Hisa Sensei subsequently denied. Tsuruyama did have a legit 8th dan from Hisa Sensei. It seems that Tsuruyama retracted the menkyo kaiden claim and then after Hisa Sensei's death, started claiming it again. He also claimed to have had some association with Kodo Horikawa Sensei, which Horikawa Sensei denied.
I guess the debate over these claims was part of the reason for the controversy... From Chris Li's post, it appears that there are further questions of Omiya's relationship with Tsuruyama.
Also, for whatever it is worth, "Shiro Omiya" is a apparently a pseudonym.
There does seem to be general consensus that the content of the book is solid from a "basics" point of view, especially for aikidoka who wish to gain a glimpse of the surface level of Daito Ryu.
When e-budo comes back, for more details (probably more than you want), the thread was:
Meanwhile, there is some information to be found here: