Please refer to MKL licensing FAQs- http://software.intel.com/en-us/articles/intel-math-kernel-library-licensing-faq/#eula2
(copied relevant Q&A below)
Do I need to get a license for each machine being used to develop and test applications using Intel MKL library?
The number of licenses for Intel MKL that you need are determined by the number of developers in your organization. These can be deployed on any number of machines on which the application is built and/or tested as long as there is only the number of licensed copies in use at any given time. For example a development team of five developers using ten machines simultaneously for development and test activities with Intel MKL, will be required to get ten licenses ofIntel MKL. View the EULA for complete details.
From the above explanation, its clear that single license is can be installed another machine for nightly build process. Assuming that, you are developer is not using same license during nightly build process.
Summarizing above points; at any point of time, only one machine (either developer or build process) will be in use. Right?