How toxic is disilanol?
Difficult to say. After a fair amount of Googling, I was unable to find any reliable sources on the compound you ask about, $\ce{H3Si-SiH2OH}$. From the Wikipedia article on silanols, it appears that the simple silanols are not stable, but no reference is provided.

It stands to reason that if $\ce{H3SiOH}$ is not stable, there is a good chance that $\ce{H3Si-SiH2OH}$ is also not very stable. Disiloxane $\ce{H3Si-O-SiH3}$ is much more stable, and silanols likely convert into siloxanes. 

Good knowledge about the health hazards of a substance requires thorough investigation, which is not possible when the substance is not stable. 

Alkyl silanols, like trimethylsilanol are stable and used for a variety of applications. Acutley, trimethylsilanol(pdf) is a volatile liquid that irritates skin, eyes, and mucus membranes (e.g. the lungs). The language on the MSDS is "may be harmful if..." This language suggests that you want to avoid contact with it but that some exposure will not cause serious harm. Note the msds for ethanol(pdf) has much scarier language.