The use of C11 language features on Epiphany depends on GCC support for those features (and also support for e.g the Epiphany newlib implementation). According to
http://gcc.gnu.org/onlinedocs/gcc/Standards.html C11 support is far from complete and I am not sure if C11 threading is part of what is already supported. As we bring the tool chain up to date and stay in sync with updates to GCC, any improved support for this will also be usable on Epiphany, but for now I'm not sure.
Short answer: don't see why not, but not sure what upstream tool support there is yet.