Is it advisable to upload theses to the arXiv?
There doesn't seem to be any real restriction on publishing theses of any kind to arXiv. Therefore, whether you choose to do so is a decision that should be made between you and your advisor, taking into account any regulations your school may have. If your work has been funded by an external agency or company, you should also take their requirements under advisement.

However, so long as your topic falls under arXiv's category guidelines, and there are no restrictions preventing you, there isn't much to lose by submitting the final version of your thesis to a public repository. It would ensure far greater visibility for your thesis than if it's left on your university's website alone.