I wouldn't be surprised to are converts. It should be difficult to adapt to another belief system and ways of life. Picture yourself trying to become like someone who is Amish or Jewish.
Yes, they are many American Sikhs, Dutch Sikhs, white and black Sikh, Punjabi and Afghan Sikhs etc. We do have Chinese Sikhs.
Read this about some converts:
http://www.sikhnet.com/news/white-sikhs-foreigners-who-found-faith-sikhism
http://www.sikhmatrimonials.com/sikhnet/discussion.nsf/78f5a2ff8906d1788725657c00732d6c/b1d2f3244f3b9f1b872565b10062131a!OpenDocument
In fact one Spanish who changed his name after joining Sikhism to Babeka Singh has done something which is very hard. He did translation of Guru Granth Sahib in Spanish. During this time he was suffering with severe cancer but this did not hinder his work. He finished this before his death. He was a very proud Sikh. Salute to his services for the Sikh nation.
http://www.sikhnet.com/discussion/viewtopic.php?f=10&t=972
Yes my dear ask er, they are in huge number, just search on Google 'conversion to Sikhism' and you will see results. Even great learned people from other religions have converted to Sikhism. In Amritsar Punjab India (where there is Golden Temple the main enshrine of Sikhism), a colony of American Sikhs is there, who not only converted to Sikhism, but also settled there. History is the witness who so ever non-Sikh gone in deep study of Sikhism, inspired to convert into that.
The reason is its high moral, ethics and virtues, believing in one and only Lord God, the unique default scripture of true Guru, Guru Granth Sahib, the holy book of Sikhism wherein answer of every question can be find, the scripture is most scientific and agrees big bang and evolution, but the cause of all the causes is supreme Lord God, You may study that holy book here:
http://www.srigranth.org/servlet/gurbani.gurbani?Action=Page&g=1&h=1&r=1&t=2&p=0&k= 0&Param=1
Here is a unique message for the people of all religions.
Of all religions, the best religion
is to chant the Name of the Lord and maintain pure conduct.
Of all religious rituals, the most sublime ritual
is to erase the filth of the dirty mind in the Company of the Holy.
Of all efforts, the best effort
is to chant the Name of the Lord in the heart, forever.
Of all speech, the most ambrosial speech
is to hear the Lord's Praise and chant it with the tongue.
Of all places, the most sublime place,
O Nanak, is that heart in which the Name of the Lord abides. ||8||3||
ANOTHER UNIQUE MESSAGE:
IF WE ARE NOT GOOD, NO ONE IS BAD.