No, it's not a requirement. We use many sources to get the full data on your backlinks.
But there are many benefits to connecting it, as you can see here:
https://monitorbacklinks.crisp.help/en/article/what-are-the-benefits-of-linking-to-my-google-analytics-account-ixu6y2/?1550922427999
To add a domain without connecting Google Analytics, just:
go to Add New Domain: https://monitorbacklinks.com/app/domain/add
click on "Add Without Analytics" button:
But there are many benefits to connecting it, as you can see here:
https://monitorbacklinks.crisp.help/en/article/what-are-the-benefits-of-linking-to-my-google-analytics-account-ixu6y2/?1550922427999
To add a domain without connecting Google Analytics, just:
go to Add New Domain: https://monitorbacklinks.com/app/domain/add
click on "Add Without Analytics" button: