No, you do not need to have a Trust Account to use PEXA. You have a number of options:
If you do have a Trust Account that is integrated with PEXA then you must use this if you wish to contribute source funds to a Financial Settlement.
If you do not have a Trust Account (or have one which is not currently integrated with PEXA) then you have the option to use the PEXA Source Account to provide source funding – read more on this here
You can participate in any PEXA Workspace without a Source Account linked to your Profile. Without a Source Account, you can lodge any document supported by PEXA as a standalone lodgement or participate in a transfer Workspace noting that you will not be able to contribute source funds on behalf of your client.
Note: If you elect to join PEXA without using your Trust Account or registering for the PEXA Source Account, you can always add a source account at a later date.