The same restriction applies to "normal" All Line Passes (and Silver Status Passes for that matter), though holders of those have the option of paying a berth supplement.Exclusion of the sleepers is a bit of a surprise - and a spanner in the works!
Other restrictions are per the Staff Travel Restrictions in the Rail Staff Travel section of the RDG site: https://www.raildeliverygroup.com/rst/where-can-i-go.html#Restrictions
Incidentally, the competition URL given in the staff brief is http://nationalrail.co.uk/goldenticket. Anyone having problems with the link provided earlier in the thread could try that instead.