No, merge tags can only be used in marketing messages (emails and or SMS), they will not work in transactional emails.
Transactional emails have and use variables, like {{user_first_name}}, {{contact_email}}, {{class_name}}, that are connected to values already set up and saved in a studio customer's Mariana Tek site account.
If you would like to know what variables are available for Mariana Tek in Xplor Transactional Email templates, check out this other help article.