I have flash as a headers on both http://www.damosoft.co.uk and http://www.diamondheartfoundation.org.uk on both sites I just simply modified the tiki-top_bar.tpl file to include it. If you want to include flash content in a wiki page, you will need to create yourself a wiki plugin to display it. its on my todo list, but very low priority. The recent changes to help prevent attacks again a tiki site and its server have stopped embed and object from being included in any tiki area as HTML code.
Safety rules Im afraid.