Yes, you can, but you cannot log into different accounts at the same time. Besides, it is normally unnecessary to do so if you want to manage more than one thermostat using the app, because one user account can associate with a maximum of 12 thermostats. However, one thermostat can only be associated with one user account. If your family members or colleagues want to manage the thermostats, you can share the account info with them.
See Account creation and pairing for more information about account creation.