The person at your registrar is incorrect. They CAN configure glue records, but if you are using Linode for DNS, then you do not need to create Glue records for the domain hosting MiaB.
Nah, don’t try that. As you can already tell, it isn’t going to work well.
Send me your MiaB hostname and the domain name for your website in a PM and I will help you straighten out the records.