Yes, you can also create ‘anonymous’ participants so you can track spending of others without them having the app. Under List info, choose ‘Add participant’, enter a name and tap the blue + button and finally the ‘Add participants’ button.
You can also create participants this way in advance, enter expenses with / for those participants and then invite them to the list. If they accept the invitation, they can choose their own name so that the expenses already entered will be linked to their account.