Ask Mr. Smarty Plants

This sounds like a real challenge! I'm not sure any plant is going to be able withstand a heavy periodic downfall of water.  You best bet might be to consider adding a layer of attractive gravel or larger stones to the area that receives the impact of the falling water.  The water would penetrate the rocks and still provide moisture for your plants.  If you don't want to use gravel-type rocks, you could consider larger decorative stones that would serve as a splash area to spread the water and keep it from impacting the soil. Here in Texas we might use honeycomb limestone, but such rocks are probably not easily available to you in Massachusetts.  However, they might be available at an aquarium store.   Here are some photos of landscapes using rocks of various sizes/colors/shapes. 

You might be able to use a groundcover in the area if you protect it while it is getting established.  You could build a frame above the plants with a permeable (to light and water) material over it that would break the impact of the falling water until the plants are well-established.  Or, you might plant a groundcover around any rocks that you add.  If you decide to try a groundcover with the rocks or alone, here are some possibilities that are native to Massachusetts:

Asarum canadense (Canadian wildginger) is very similar to Asarum europaeum (European ginger), but is native to North America.

Gaultheria procumbens (eastern teaberry) is a very low shrub and is evergreen.

Mitchella repens (partridgeberry) is a low evergreen herb.

Cornus canadensis (bunchberry dogwood) is a low perennial that has attractive flowers in the late spring and summer and red berries in the fall.

Fragaria vesca (woodland strawberry) is a low perennial with edible fruit.

Sedum ternatum (woodland stonecrop) is a perennial low-growing succulent.

Here are photos from our Image Gallery:

Asarum canadense

Gaultheria procumbens

Mitchella repens

Cornus canadensis

Fragaria vesca

Sedum ternatum