Buddhism's methodology is trying to make people aware of that what they are not instead of giving them informations of what they are. But this doesn't mean that Buddhism denies some of the other traditions view of the universe. I watched Thich Nhat Hanh's dhamma talks and he said many times that "we are waves in an ocean". So in a practical sense, every meditator can come to this point. Especially If you reach to the really advance stages in your spiritual path, you start to be more aware of the spiritual essence of things than their form identities all the time. And ofcourse, the experience of Nibbana itself will lead people to this "oneness" idea easily. I think there is nothing wrong with that If you are deeply involved in the practical side of the Buddhism: Which is meditation/mindfulness.
I think the reason for Buddha's methodology of telling people what they are not is to avoid people's tendencies to make the spiritual path to a belief/worshipping based religion. For example he used words like "Emptiness". "Nibbana". You can not worship Emptiness, Nibbana..You can only worship the god. Maybe Buddha's methodology saved Buddhism from transforming to a dry/harmful religion like some of the other religions that most of us know. This doesn't stopped many Buddhists misunderstandings of the core of the Buddhism but the core of the teachings of the Buddha is still alive and being practised by many monk and lay people in the world. And this leads to some people's complete freedom from suffering. So these things proves that this methodology works well. The vast majority of the humans will never get involved with true spirituality but that is not Buddhism's fault.