I own a Danner 9.5... The MFG. care and operating instructions and box indicate both inline and submersible, Fresh and Salt water They make no recommendation either way.
I know what Grog is referring to, there is a Online Mega store the has a note on the Website about no inline Salt, but the MFG doesn't note it in their instructions.
Now there is a little slip of paper on product update they throw in the box that you don't see on the WEB sites. It state you "Must remove the impeller assembly approx every 6 weeks in order to remove Calcium and Mineral deposits using the following procedures; Blah blah blah. This is on Saltwater or Hardwater Applications."
Anyway, I have mine submerged....
PS the Mega site has the fitting sizes wrong, also. They are 3/4" threaded on both ports