I practiced yoga diligently until this knowcked me out. I would take it easy on the standing poses, and certainly not hold them as is usually practiced. Take them for a moment and then kneel down.
Otherwise, the yoga can be helpful for healing blood and energy flow, positive outlook, and maybe mechanical therapy involving the whole body (a posture problem anywhere will 'ripple' down the body into the feet, so yoga on the rest of the body can help the feet).
About the cramp, which I got sometimes and now I have feet problems get often, this can be treated several ways:
One, do the counter-stretch:
(THIS FASCIA STRETCH I HAVE NEVER SEEN POSTED BEFORE)
On knees, with feet together, toes curled under feet, so butt is on heels and body touches ground at knees and ball/toes of feet. Inch the kness forward to a mild stretch, relaxing the weight into the heels, and lifting the chest upward, with steady, smooth long breathing.
My modification of this yoga stretch eases up on the big toe area, which I hurt using the FOOTFLEX linked on this board (see other posts about this danger): with toes together, arc heels outward and let wieght fall between them (gently). Now the stretch is in the other toes and big toe is not invloved.
One can do it both ways for different emphasis.
TWO: definitely do toe crunches and towel curls to strengthen this area. These might lead to cramping, but it is something to work through.
Three: with legs out straight, point big toes together and try to make soles face eachother and little toes touch (porbably not possible with legs out straight). This should lead to cramping which you then ease off, concentrate the mind on relaxation of that area, and then repeat. You need to work on controlling a relaxation response in this area, as well as stretch and strengthen it.
These exersizes in conjunction with regular calf stretching should help alot with the problem you describe and keep you going with yoga and further healing, so long as there are no other complications to your foot problem.
Remember not to hold standing poses, and also never do balance poses at all: just kneel down and do the kneeling stretch gently until the class moves on to the next thing.
good luck, alan k