skin-so-soft is safe to use on pets as far as i know, however, it won't help their dry skin.
what are they eating, and are you supplementing them with anything? how old are they, and do they have any health conditions?
dogs can have dry skin for a lot of reasons, including endocrine (thyroid issues), environmental (dry heat, etc), dermatologic (skin issues that result in a lot of scratching).
you can try including in their diet some fish oil and such, but that just masks the problem in some cases. you can also look into some moisturizing sprays (humilac comes to mind, but it smells awful IMO in the bottle!), shampoos, and conditioners. a change in diet may also help, or a humidifier.