Not only will they grow in FW, they'll thrive.
The SW aquariums they do best in are the ones that are most poorly maintained. Not many plants do well in systems whose goal is to achieve zero nutrients. Hence most are seen in refugiums rather than displays.
At the very end of taking down my last reef system in the fish room. The last bit of livestock I had was about 15 or 16 mangroves that were at various stages of growth. I'd read conflicting stories about acclimating, death in FW, but none seemed to come from any real experiences. So I finally decided to just stick the last five or so I had left into my first planted tank. No acclimation or nuthin, and they've flourished for a couple of months now.
There's lots of theories people put out there without any sound logic. My favorite was the one about mangroves destroying fish tanks because the massive roots will eventually cause the tank to burst. Good lord, if I live long enough to see that happen I'll be a happy man.
One of the neat parts of mangroves is the root structures they form. If you can or desire to, you can try to suspend the mangrove pod in mid-water. The thicker root structure will reach for the substrate and form a natural driftwood-type aquascape. It's not a swift process though.