+1 although it isn't that important to me, I'd like to know these things too. however, the docs are complete in terms of listing all possibilities -- to find out the capabilities you'd have to try out all the possibilities on your own. please do so. there's no way such software-experiments could destroy your board (and I bet if there is, then just for discovering that bug adapteva would give you a new board).
also you should read the zync-arm-docs (not provided on the adapteva site afaik). epiphany naturally cannot trigger anything on arm because technically it's just some hardware attached to fpga and during creation of the arm-processor the epiphany never was part of the design. however, maybe in the zync-arm-docs you could find a way how fpga or memory-writes could trigger something on arm anyway. and if there isn't. definitely there is such a possibility in fpga and you just need to code it there. so, please stay curious and explore!