Can I concurently access a database with embedded and with regular server?
This FAQ is about FB embedded on Windows, Linux embedded is not covered here.
If you mean it's one database and two applications then: NO
If you mean it's two databases and one application then: YES
Firebird embedded is actually a regular Firebird client with server capability. This means it can be used to connect directly to a database file (embedded) and simultaneosly establish a connection to a Firebird server somewhere on the network (or on local machine via 'localhost'). You can do this if you wish to copy data from embedded database to the 'real' server and vice versa.
Since each Firebird server holds a lock on the database file, you cannot use a single database file with embedded and access it with regular server at the same time. If you could it would lead to database corruption very quickly.