You bet. There will be annual declarations and maybe more.
Chapter 8 of the government's RHI announcement says
In addition to the up-front checks, participants will also be required to provide information and confirm that they are still meeting the relevant rules and will do so for the duration of their participation in the scheme.
In addition to the regular annual declaration, Ofgem will be able to make ad hoc requests for information where it is concerned or suspicious that one or more of the eligibility criteria are not being met or as part of a random or targeted audit.