Hey! Fisheye isn't a version control system, it is a version control system viewer. So you point it at one or more version control systems you have deployed.
However, to guess what you're asking, then yes. The majority of version control systems commonly connected to Fisheye default to non-locking mode.
Subversion for example is one. (That could be setup for locking, but by default isn't)
Other version control systems like git and mercurial don't have the idea of file locking to begin with