Hemlock is very shade tolerant.

Japanese maples are ideal choices for this type of planting.....accenting a water feature is a very common placement for a weeping JM in an Asian-inspired garden. And most are very shade tolerant and actually prefer to be in more shade than sun. Red leafed ones tend to lose coloring in a lot of shade so unless you don't care about that, selecting a green leafed form may be better.

One of my favorites is Acer japonicum 'Green Cascade' - a very graceful weeping habit, wonderful delicate foliage and some splendid fall color with sufficient filtered sun.

Here is a link that might be useful: Acer japonicum 'Green Cascade'

Also consider weeping redbud.