It is interesting what your father has said on this topic. I recently was faced with a similar questions about Muslims. I have enquired about this and the answer is that the Muslims that were on the Guru's side were Sufi Muslims who themselves condemned the actions of the more radical Moghal Rulers. The Sufis were God fearing devotees who saw the rest of humanity in the same way prescribed by Guru Nanak.
In terms of the radical extremists similar to those around today then they are the ones that will be deceitful.
As a rule of thumb I would air on the side of caution and not trust any Muslim unless you have strong reason and evidence of their nature.
