Most Siki's that I know state this pretty clearly that there is one God, one source. This is Sikh doctrine as far as I'm aware.
(no, I'm not debating...mods who removed my post...)
Yes, in Sikhi there is
Ik Onkar, one universal creative force. It goes further in a way that Aupmanyav alluded to; Sikhi is panentheistic so that everything in existence is essentially formed from god itself - like a wave (an object in creation) is simply water in the shape of a wave, that tumbles down to merge with the water again.
However, waves are still waves. The illusion is in thinking the wave is in-and-of itself a wave. It's not - it is water. And the water is God. The Sikh's mission is to constantly have simran (remembrance) of this fact. This is the essence of reality.
Sikhi emphasises the oneness and absolute pervasiveness of this Ik Onkar and goes as far as to say that gods and goddesses are rooted in / products of Maya and that they, too, yearn for Ik Onkar and sing at Its door with the rest of creation.
At the same time Gurbani does sometimes equate gods together - for instance, equating Raam and Allah together.
So when you say "all gods are one", what does that actually mean in a Sikh context?