Lancelot I see as tilting the scales seriously towards bisexual on the Heteroflexible scale. Raised by Faeries. Mad for Guinevere and also Plainly in some sort of obsessive romance with Arthur.
Where Tokiomi is concerned... well he does love a Classy Lady! He's married, which happens luckily to be his pleasure as well as his duty, and enjoys "married life" immensely.
HOWEVER I do see him as Heteroflexible. He's a curious person by nature, so I wouldn't rule out same-sex experimentation before marriage. He's also a Mage and a Pragmatist where Magic is concerned.
Yeah, I think Tokiomi would keep his eyes open while doing just about whatever he had to do in the course of his Quest for the Grail/Root. I also think he'd enjoy it - even if he never let on.