I decided to write this post since there is not much documentation related to getting the customer group id for a coupon.
The best way to achieve this is to grab the customer group id using the function getCustomerGroupIds().
Below is a simple and fast way to get this using the salesrule/rule model.
Now you can call your function and grab the customer_group_id for each coupon.
Hope this helps someone out there!
Perfect, thank you for this!