Fateh,
Whether you call that One God Allah, Waheguru, Yahweh, Brahma, God or Raam, Sikhs still believe in that One God. The Guru Granth Sahib starts with Ek Oankar (literally meaning 1 God).
Also, most people naively assume that Sikhism is just a mish mash of Islam and Hinduism. While some concepts are similar, Sikhism is a revealed religion. When you read the Guru Granth Sahib, Guru Nanak makes this very clear (khasam ki bani - the word of God -
www.srigranth.org). Unfortunately, as no one in the West has seriously studied Sikhism until very recently, most of the colonial views on this faith have persisted to this day.
Jindi Singh.