If I were you, I'd rather use pantheistic than polytheistic.
These categories are frankly too narrow to fit Hinduism. Hinduism is simultaneously pantheistic, polytheistic, monotheistic, and monistic. And yet it is beyond these narrow categories.
Wiki define Polytheism:
Polytheism is the belief of multiple deities also usually assembled into a pantheon of gods and goddesses, along with their own mythologies and rituals.
From this definition, Hinduism is polytheistic.
Consider the definition of Pantheism:
Pantheism is the view that the Universe (Nature) and God (or divinity) are identical.[1] Pantheists thus do not believe in a personal, anthropomorphic or creator god.
From this definition, Hinduism can be considered pantheistic but Hinduism admits a creator God.
Lets come to the definition of Monotheism:
Monotheism is the belief in the existence of a single (one) god.
There is a belief in a single God. However in Hinduism, He/She is not defined as being jealous of other Gods because there cannot be other Gods.
Monism is defined as:
Monism is any philosophical view which holds that there is unity in a given field of inquiry. Accordingly, some philosophers may hold that the universe is one rather than dualistic or pluralistic.
By this definition, Hinduism is monism.
When you quote upanishads to stress that Hinduism believes in One God, you must be aware that the very same Vedas talk about individual deities. Then, there are so many Puranas and Itihasas which describe various God and their individuality.
Therefore, Hinduism cannot be bracketed into any of these categories because Hinduism has qualities of all these categories. Hinduism is far beyond the comprehension of those who created these self-serving categories.