"FLV" as a format could use the following codecs to compress video: On2 VP6, Sorenson Spark or H.264. Which one are you looking for?
If you are wanting to use a frontend SWF to act as a player for the FLV file, try simply changing the file extension to FLV.
I have DW and used it to insert an "FLV" that was simply an H.264 MOV with the extension changed to FLV. Played fine. Flash looks inside the file to determine if it can play it rather than looking at the file extension. I changed the file extension to FLV just because DW wouldn't do its thing without that step.
Using a player like JW Player, I could do this without even changing the extension.