As long as you can 'eyeball it' so the camera is visually level you're fine.
Using an actual level (either a bubble level in the QR clamp or a simple horizontal level) is fine but unnecessary since the Matterport camera can tolerate up to 15 degrees off level.
Remember to invest in a high-quality, professional tripod and clamp. Learn more.
Low quality tripods and clamps (such as ball-head mounts) causes most hardware-related scanning problems.