I don't have any experience with blue hygro, so in lieu of a response from someone with direct experience, you are probably fine letting it grow in the air.
There are very few obligate aquatics on the market. That said, it is common for plants that break the surface to stop producing underwater leaves. Just keep that in mind when considering the asthetic you are going for.
As to the second question, I generally advise only shrimp in a tank that small, or a betta.
I would would not be comfortable keeping fish in a tank that small, but conceded that with proper maintenance endlers livebearers or celestrial pearl danios would probably do well in that setup.
Sent from my SM-N920V using Tapatalk