To Mystics (Sufis) all faiths have inner truth in it, all faiths are sacred. That includes Hinduism. Sufis who strongly believe in Oneness of God, how do they appreciate Hinduism which apparently talks about many gods? Thats why many orthodox religious people find it surprising! Well, basically that surprise comes because most of us (so called non-hindus) have very negative understanding of Hinduism (thinking it as polytheism is the main problem, whereas Hinduism is basically a montheistic faith, believing in One Supreme God). Interestingly Hinduism is a very important philosophy in terms of spiritual understanding and the understanding of God. As one of the most ancient philosophy and religion it holds great teachings for mankind.
If we go to the roots of Hinduism we can see the Unity of God is also spoken. The sages of Hinduism at different ages did acknowledge the Unity of God in the sacred writings. When i was reading Yann Martel's Life of Pi, i came across this beautiful writing where he describe Hinduism in a nice way. I would like to post it here.
"... There is Brahman, the World Soul, the sustaining frame upon which woven, warp and weft, the cloth of being, with all its decorative elements of space and time. There is Brahman nirguna, without qualities, which lies beyond understanding, beyond description, beyond approach; with our poor words we sew a suit for it - One, Truth, Unity, Absolute, Ultimate Reality, Ground of Being and try to make it fit, but Brahman nirguna always bursts the seams. We are left speechless.
But there is also Brahman saguna, with qualities ... Brahman saguna is Brahman made manifest to our limited senses ... everything has a trace of divine in it. The truth of life is that Brahman is no different from atman, the spiritual force within us, what you might call the soul.
The individual soul touches upon the world soul like a well reaches for the water table. That which sustains the universe beyond thoughts and language, and that which is at the core of us and struggles for expression, the infinite within the finite.
How Brahman and atman relate precisely? ... atman seeks to realize Brahman, to be united with the Absolute, and it travels in this life on a pilgrimage where it is born and dies, and is born and dies again, and again, and again, until it manages to shed the sheaths that imprison it here below.
The paths to liberation are numerous, but the bank along the way is always the same, the bank of Karma, where the liberation account of each of us is credite or debited depending on our actions.
This, in a holy nutshell, is Hinduism."