If you UTFSE, you'll discover this very question was recently asked and answered:
The original poster provides a link to the owner's manual for they Yammie. In post 12 I state that it will work fine and should mount fine on the TD-9 rack.
As for the rest of your questions, I don't have an answer on the FD-8 question, maybe Bruce (BarT) will see this and opine. Regarding the rack stability, yes, if you strap it to the rack, that part of the equation will be stable. The only question then is how stable is the rack setup itself. Remember, you'll be putting some added force onto the rack via your foot action transferred thru the HH stand to the rack. I mean if you're some hyper-animated drummer, for all we know you hammer that pedal. Heh heh, OTOH, I don't think it'll be an issue.
Mix and Match Heaven: TD-12 or EZDrummer, Diamond Drum 12" snare, Hart Acupad toms, Roland CY-5 mounted on a Hart Ecymbal II Pro Pedal, Hart Ride, Hart Acupad 8" bass, 2 Roland CY-14 crashes, two Concept 1 cymbals, a Yamaha PCY-10, all on a red Roland V-Sessions rack. Pads on hiatus: PD-7, Kit Toy Splash, Hart single-zone HH, Alesis DMPad ride and an entire Concept 1 kit.