There is no such thing as a neutral definition of a cult. It is a purely subjective and derogatory term. The definition you found which includes "unusual doctrines not found in commonly accepted religions or philosophies" is a perfect example of this; by this definition, Copernicus would have been considered a cultist during his own lifetime.
To make your question more objective, we might ask, what elements of American society object to Science of Identity Foundation, and what elements accept it? This is much easier to document.
Science of Identity Foundation self-identifies as Hindu, and Gabbard claims its founder is "essentially like a Vaishnava Hindu pastor." These claims have been accepted by far-right Hindus. Specifically, Gabbard has been funded by the American Sangh, the American branch of Rashtriya Swayamsevak Sangh (RSS), a fascist group that regularly sponsors violent attacks on Christians and Muslims.
LGBT groups in America have proven less accepting of Science of Identity Foundation. According to Iowa Informer, "Many in the Hawaii LGBTQ community say they consider Gabbard’s apology insincere, as she continues to serve and worship" the group's guru, who according to a quotation of his retrieved by the Informer, "refers to gay people as 'cockroaches' who should be exterminated."
In conclusion, some Americans find Science of Identity Foundation an appropriate match for American society, while others firmly reject its teachings.
