Yes, a user can subscribe for in stock notification for the Configurable product in Out of Stock Notification for Magento2.
If a configurable product is out of stock, then out-of-stock notification works the same as it works for a simple product. A user just has to select an associate product, enter his/her email id and click on Notify Me.
A user will be notified by email when the associate product gets back in stock.
Please do contact us for any further queries or requirements. You can also check our Magento 2 Extensions for additional features.