This is an excellent question. What angels do you have in the reef?
From experimentation in the LFS, I've found that butterflies are not interested in the grasses. Of course you could always 'luck out' and get the one butterfly that decides he prefers vegetable matter, but from the species tested, few of them were interested. Not much more than a nibble (which may have been an effort to eat epiphytic growth in fact) from them as a group.
The angels are a different matter. Juvenile french angels were very interested and devoured Halophila, and ate a good bit of Halodule too. I didnt offer them turtlegrass. I think many of the larger angels might take a shine to the seagrass. But I also think its worth a little experimentation. Unfortunately I have not been able to experiment with other large angels except a bi-color, he also nibbled the Halophila and Halodule.
Pygmy angels like potters, flame and the argi complex didnt really notice the seagrasses. They went wild for Ulva, Chaetomorpha, Gracilaria and Halymenia though. I'm not sure if I had left the grasses in their holding tanks longer if they would have eventually eaten them or not. I have been considering adding a C. argi to my tank or to future seagrass setups.
We need more people to try them out with the plants.

A seagrass tank might make a really nice display for these fish that are not reef safe. I wonder if they are really well fed if the occassional grass grazing is really detrimental, much like those reefers who keep butterflies that are model citizens except for a few polyps each month. Not enough to do real damage.
Definitely keep us updated if you try out any combinations of the angels/BFs and grasses.
>Sarah