I guess they can be considered as Hindu as per the core beliefs. Religion is considered a personal belief in Hinduism and followers are free to choose the different interpretations within the framework of karma and samsara. Even an atheist is considered part of Hinduism. Hinduism is not a structured religion having set of rituals, or one or few holy books and a set guidelines. The term Hinduism itself is not correct as it was imposed later on. Hinduism includes a diversity of ideas on spirituality and traditions, but has no ecclesiastical order, no unquestionable religious authorities, no governing body, no prophet(s) nor any binding holy book; Hindus can choose to be polytheistic, pantheistic, panentheistic, pandeistic, henotheistic, monotheistic, monistic, agnostic, atheistic or humanist. Ideas about all the major issues of faith and lifestyle – vegetarianism, nonviolence, belief in rebirth, even caste – are subjects of debate, not dogma. I agree its difficult to understand even for me. The term Dharma is more apt then the term religion for such beliefs.