I suspect it's Linux-based with Java. And it's a Web-based service, so it
should be platform-impartial w.r.t. the clients.
Speech Recognition Software Adoption Powers Voice Applications
Around the World
Web-Based Platform Revolutionizes Voice Business
There is another company that makes Linux-based voice recognition servers:
Wizzard Software Releases WizzScribe SI For Linux
Microsoft is getting closer...
close, but no cigar (the infamous "Dear Aunt" video).