Yes. Once your template is linked to an email list, you can add merge fields within text content. Note that merge fields are generated from the grid and the data on the grid where it was created. For example, if your email list was created from the Event Grid, you will see fields associated with the event grid as shown in the image below.
If your list was created from the Constituent Grid, you will see fields available in the Constituent Grid, but you cannot see event fields.
If you combine lists from multiple sources, you may see fewer fields available for mail merge. Also, be cautious about which fields you insert because there may not be data in those fields in some of the lists.