Viera are not female only. There are indeed male Viera just never seen because the male Viera live in their own tribes away from the females and are more reclusive. This is said in FFXII.
Also, there is nothing stopping the development team from just making Viera barefoot for a large majority of shoes. Re-model some of the more popular sets and make all the others like leveling gear just simple straps or such. This was used for TERA's Amani feet and is actually vastly preferred to their method they use now (of squishing their big feet into tiny high heels).
