What are Basic user's rights, if he is a part of pro account ?

Zoom user types & roles

Basic: A basic user is a user without a paid license. Basic users can be on Basic (free) plans, as well as paid plans such as Pro or Business. A basic user on a Basic plan can host meetings with up to 100 participants. A basic user on a paid account inherits the account's default meeting capacity, such as a Business account's default meeting capacity of 300. If 3 or more participants join, the meeting will time out after 40 minutes. They cannot utilize user and account add-ons such as large meeting, webinar, or conference room connector.

See:  https://support.zoom.us/hc/en-us/articles/201363173-Zoom-user-types-roles