I fully agree with your comments that the Energy Discount scheme should be available to all.
The scheme was reserved to the UK Government which has published advice on how anyone who did not have a domestic electricity meter and contract with an electricity supplier could apply for the £400 support. This is available on the link provided below.
The Scottish Government remains committed to ensuring equality of opportunity for all of Scotland's Gypsy/Travellers, a particularly marginalised group.
The SNP will continue to work to ensure equality for Gypsy/Travellers by integrating their needs into policies such as health, education and social services.
https://www.gov.uk/get-help-energy-bills/offgrid-park-mobile-care-home