Yes, and you might try and export, move and import them, but that is not as easy as setting up an IMAP account and move the messages using that account. (Then you might discard the IMAP account once the messages are moved.) 🙂
The thing is, you set up the IMAP account in Thunderbird first, then move all your messages to the IMAP server, then set up the IMAP in Mail, and voila, all the messages are available... then you can download the messages to a folder/mailbox and then decide if you want to keep the IMAP account or not... 😉