Depends. :p
If DB'd with Bw (S), they always shoot as (S).*
Otherwise they count as (S) if shot at by Bw or naval and they [sc. the Bw (X)] score lower. IOW, you get the defenisve +1 on scoring less, but not the offensive +2 on scoring more.
It may be noted you don't get the +1 when shot at by WWg. This might be because Hussite ones had a variety of firearms (you don't get the +1 against Art or Shot either) but seems somewhat odd wrt earlier WWg (S or O) whose crews would use bows or crossbows only.
* I believe the only lists with Bw (X/S) DBE's are Alex Imperial and Burgy Ordonnance.