I know nothing about a Aviva Expert, but I do use a Dexcom G6 with a Omnipod. They do not communicate although there are rumors by next year they might.
The G6 just reads your numbers all day. It doesn't have anything to do with deciding doses of insulin etc. It keeps track of trends, whether your sugars are going up or down or stable. It also lets you know by graph how your sugars are doing each day.
Is that what you wanted to know? I am in the US, so it's possible something is different from the UK?