Generally yes. If a member of another system will accept your BrisLETS cheque, hand it over with a smile. Some systems accept our cheques and others don't.
You can accept a foreign cheque in any foreign currency at any time, and send it in to your own BrisLETS Secretary.
There are dozens in Australia, but some are hard to find. There is a good page of links here. It also leads to international links.
Each LETSystem should have a single InterLETS a/c in their system. When Buggsy from Vegas LETS/ KalLETS or wherever comes to Brisbane they can, if they have a current membership of a LETS anywhere give you a check for the amount of "Bones" for you to put in to BrisLETS bookkeeper for the trade. This is debited or credited to your a/c from the single InterLETS a/c in BrisLETS. They put in an identical check to their own bookkeeper when they return home.
Spending BrisLETS Units is easy too. Suppose you go to Kalgoorlie and stay overnight with a KalLETS members, and that member agrees to accept your BrisLETS cheque. Make out two identical cheques, one for each LETS system involved in the trade..