When making bread dough, can sugar and salt solutions be used or should the sugar and salt be added dry?
Either is fine, so long as you account for the liquid.
I normally add dry sugar or (rarely) salt at an early enough stage that the "proto-dough" is effectively still liquid and they will quickly dissolve, so it makes little difference. If adding at a later stage, a solution might be preferable for even distribution. Bring on the uptight bakers claiming you can't add stuff later (guess what, it still comes out bread...) And, of course, when using honey, molasses, or syrup, it's a solution whenever you add it.
Why would you want to? If you did (I can't see it being a problem), you would need to reduce the amount of water equal to the amount of solution you are using, so as not to over-hydrate.