Hey James,
Yes, WP Webhooks also supports most of the Metabox features.
To make it work, you can use the manage_meta_data argument, which is available with the create_post and update_post webhook actions.
This argument supports a JSON formatted string, containing al lof the meta data you want to add or update. For convenience, there is a meta value generator (specifically for the manage_meta_data argument) available here: https://wp-webhooks.com/blog/how-to-update-custom-post-meta-values-with-wp-webhooks/
Please note: To make it work, you need the meta key of the meta value you would like to update. If you want to add multiple meta entries with the same meta_key, you can change the update_post_meta key to add_post_meta. If you want to add or update a meta value, simply use update_meta_data. To delete meta values, use delete_meta_data.
