Hi Jordi,
VMware Converter is not open source. The tarball you have found contains OSS that is used by Converter, not Converter's code.
Converter does not need to be installed on the machine to be converted. You can install it on any Windows machine provided there is the needed network connectivity.
OTOH, though Converter 4.0.x will probably not be able to convert SLES 11, it doesn't harm to try. (BTW, if your SLES 11 machine is with UEFI firmware, it can not be converted by any Converter version)
HTH,
Plamen