DBeaver not showing dbms_output

You can enable server output console. (Ctrl+Shift+O) If you expand the query pane, you are able to see two more buttons. (Server output console e Execution Log)

I can't really tell you the diference between this server output console and the output view tab you show on the print screen above.

Actually you can use DBMA_OUTPUT.PUT_LINE in DBeaver (mine is version 4.3.2), maybe you were just looking at "wrong" output tab. I have attached a screenshot of my SQL editor to make my point clearer.