Salt may irritate the pads making them itch and making it unconfortable for them to walk until the salt is off of their pads. Once it is off they are back to normal, avoid it if possible, if not they will still be fine.
When we lived in Vermont and it got WAY below zero, the only way the dogs let us know it was too cold to walk was to lay down and stop. They have pretty tough pads. You can use bag balm or vaseline on their pads to keep the salt off before and after the walks. Wipe them off after the walk and if they look cracked or dry, put some more bag balm on them. You can also try Muttluks doggie boots. I have heard they are really good. I always had trouble keeping boots on the dogs but never tried that brand and we don't need them anymore now that we live in NC.