Is it possible for someone to learn about God without learning about him from the Bible or another believer, such as from nature?
Well you have two questions here and there are opposite answers for each. Can you know about God without the Bible or other believer? Yes according to the Bible you can.
But then comes the title question. Is it possible to KNOW God from nature? The answer is no. Just like you can learn some things about my intelligence by looking at the way I code programs, you could never KNOW me just by looking at my code. In fact you could get the wrong idea about me completely if you only look at the actual code and don't read the comments in it! You've got to come to where I am if you want to know me. That's just logic, but what does the Bible say about that? How would we 'come' to God?
So you can know about God without help from the bible, but I don't think you can say you could KNOW God without either the Bible, or others who know Him, because in order to KNOW God you have to have faith in Jesus, and while the heavens openly and obviously declare the glory of God, they don't obviously announce the person of Jesus Christ. However, that doesn't mean that if no Bible or christian is available you can't ever know Him, God said in several places those who seek Him will find Him. For example:
But if there is scripture or other christians available and you don't consult them, how could you claim to be seeking God with all your heart and soul?
It is possible to envision the idea of God by looking to creation as you've said. It is written:
But if you want a non-biblical argument there are also philosophical arguments.
For example, Aristotle in his works metaphysics explains about the absolute substance, the "unmoved mover". He deduced this idea by observing the nature.
Another philosopher, Descartes, by observing that in nature there are different degrees of perfection in the created beings, he deduced that there must be one perfect being. If that being could not exist, then that being could not be perfect. This is known as Descartes ontological argument.
The argument goes like this (quotation from the article)
This philosophical idea has received criticism during the 20th century. But my point was to show that during the centuries, men have found themselves so amazed by nature that they could rationally conceive that God is the creator and that he is perfect.
Although, by mere rational argumentation one cannot grasp important facts about our Lord such as his Love for mankind, or to experience his love embrace and his transforming power in our souls. I think of two reasons: the first is the imperfection of the human mind, as it is written:
and the second, that there are clear limits to human understanding, and that most of it is vanity of vanities; as it is written.