Hi Alex,
it depends on your network / firewall configuration (and the possible network protocol interpretation by your firewall).
The database communication is the following: Client (dynamic ports) <-> Listener Port (e.g. 1527)
Depending on your firewall rules (and features / SQL ALG) the dynamic port issue could be a problem. The Oracle Connection Manager is usually used, if a "large" amount of databases is hidden behind a firewall and the ports should be "static".
Regards
Stefan