The "right to roam" in Wales is currently the same as in England and does not allow access to open access land for the purposes of hang-gliding or paragliding.
The legislation is enacted by the Countryside and Rights of Way Act 2000 and the section relevant to us is Schedule 2 on page 75:
1. Section 2(1) does not entitle a person to be on any land if, in or on that land, he—
(s) engages in any organised games, or in camping, hang-gliding or paragliding