Is root access a paid feature in Genymotion?

No, root access is not presented as a paid feature. The docs describe it as an available device permission toggle, with rooted access depending on the Android image and product version. See Emulated Features and Widgets and Root Access.

In Genymotion Desktop, Android 5.0 to 15 are available in the free version, and Android 16 requires a paid license, but root access itself is not listed as a paid add-on. On some newer images, root must be toggled on or is already enabled by default depending on the product and Android version in How to root a Genymotion virtual device?.