I'm not sure about a Lutron <-> X10 bridge. I've never seen one.
Lutron does have RS232 serial interfaces (like the RA-RS232 for RadioRA) for most of their technologies. This would allow you to control Lutron via Serial Bridge
and AppleScript. It will require you to write, in AppleScript, the code needed to implement Lutron's RS232 protocol, however. Once you have Serial Bridge communication with the Lutron RS232 protocol, you can use AppleScript to tie it into Indigo somewhat. By somewhat I mean that the virtual Lutron Devices in Indigo won't seamlessly work as Lutron devices but it can be hacked in there a bit. I'm working on some changes for a future version of Indigo that will let additional hardware capability (like Lutron) to be added to Indigo as a plugin, which will make this a bit better but will still require someone to write the Lutron RS232 protocol to Indigo plugin code.