yes of course you can use any other client library without such restrictions.
Note that we have two flash oriented libraries (see
http://www.lightstreamer.com/products.htm)
the one called "SDK for Flash Client Development" uses the web client library as "network layer" so that the same origin policy still applies with it
the other one, "SDK for Flex & AIR Client Development", uses the Flash player network layer so that you can configure the crossdomain.xml file to make it work across different domains.
HTH