It would be probably rejected if your theme depends on the plugin and even if the reviewer misses it, you will have bad rating/complaints about the problem and at some point, your theme will be disabled.
If you’re using a third party plugin that would require purchase, you will have to have the proper licence to sell it within your theme.
Does this mean it is not allowed? Is there documentation that mentions this? I have only found information for third-party free plugins but not for premium plugins.
This is a similar case to some Elementor template kits that require Elementor Pro, but this time for WordPress themes. On the template kit, the buyer needs to use or purchase their own Elementor Pro license.
I think same thing for your one. You have to get license permission to use the Gravity Forms plugin in your theme. and you have to clearly mentioned in your theme page that customer of your theme must have to purchase the Gravity Forms plugin license to use the plugin and this plugin is mandatory. But it will negative effect for your theme and may cause negative ratings, refund request etc.
For more information you can open a envato author support ticket.