I do not know how to check it via SSH access.
The method for detection remapped or bad blocks via UART is described here.
But come on, you have Winbond, ppl with Foresee NAND are at higher risk than you. I'd skip this check since the chance to have bad blocks is less than 1%. Up to you.
But if you feel you need to be in 100% safe mode, use SNAPSHOT for all files during the OpenWrt installation (fix for handling bad blocks is included there).