I conduct business in the USA, both sales and purchases. No VAT is paid or due on these transactions. I report to HMRC simply as part of overall gross sales and purchases. None of these companies are in the quickfile database. So I cannot add them as part of my overall business. The old way submitting direct to HMRC it was not a problem.
If you want to have them included in the box 6 & 7 totals on your vat return then they will have to be registered in QuickFile as sales or purchases respectively, though you don’t necessarily have to add each individual supplier or client if you’re not actually invoicing them through QuickFile, it could just be a dummy supplier or client record.
Personally I would record them properly just because I like to have a full record in QuickFile with receipts attached so I can quickly find anything I need to refer to in future, but if you already have your own record keeping System this may not be necessary.