If it's been made with SynthEdit 1.1, so no it is not yet x64 compatible.
Up to SynthEdit 1.1 included all the plugins made with SynthEdit are only 32-bit compatible.
SynthEdit 1.2 will be 64-bit compatible, but it is still in Alpha version, so not yet distributed for real developments by the users, only for final tests to track down the last big bugs and to improve the stability before the real distribution which will begin probably in the next months.
Also many people complain that developers of plugins made with SynthMaker or with SynthEdit don't provide Mac versions of their plugins. How could they do??? Neither SynthMaker nor SynthEdit are actually compatible with Mac! SynthEdit will be indirectly compatible with Mac only starting from the SynthEdit 1.2 once more. You can see more about it here: