The only thing that bothers me about using a product like that in the Bushwheels is that it will never leave. On the mountain bike, I use Stans all the time. About once a season you need to dismount the tubless tire and clean out the inside, then refill and remount the tire. There is usually a large ball of relatively light crystalline looking stuff (resembles a goat-head cactus only about 2" wide). That is with a relatively small volume in a 2.3" tire. In a bushwheel, you can't open the thing up, and the volume of Stans required is much higher. I'm sure it does the same thing as it dries, but it's probably lots bigger...so after a while, you've got all this crap flopping around inside the tire. It may not affect the tire too much (and yes, the manufacturer does recommend its use). For small punctures it works great. I haven't used it in the Bushwheels.
Slime is a similar product, cheaper, and generally used inside tires with tubes, but I have used it to reinforce repairs on auto, wheel-barrow, and tractor tires.
If your valve stem is gummed up, you can support the aircraft so deflating the tire will not cause it to settle too much, then unscrew the Schrader core, clean things out with a small piece of plastic or Q-tip, then reassemble.
