Are they allowed to use in a master thesis?
I would think it improbable that such things are specifically disallowed, because it's just not something that people typically try to do. Overall, the effect is unattractive and does not follow good typographical practice. If your university policy does not object, your supervisor probably would (and should).
One or two unobtrusive ornamental flourishes may be appropriate on the title page, but certainly not in the main text.
If you are struggling for ideas on the typographical style of your thesis, I would highly recommend looking at the classicthesis and memoir packages. Of course you still must obey any official policy on the formatting, but these styles can at least provide a good start that's a little less sterile looking than vanilla LaTeX.