Most of the answers say "No" but I would like to offer a different point of view eventhough it will not be popular, sorry!
The key concept of Buddhism are the 4 Noble truths. They are shared by all schools and were part of the first discourse of the Buddha, the 4 Noble truths are so important that they keep appearing over and over again in many suttas.
I cannot see how can one be a Buddhist disagreeing our doubting the 4 Noble truths. So, if you check them you will see that is not possible to agree with them and at the same time disagree with the idea ofthings like samsara, rebirth, etc
The first thing Buddha said after enlightment (is in the dhammapada) was: " I have gone round in vain the cycles of many lives ever striving to find the builder of the house of life and death. How great is the sorrow of life that must die!"
The 1st Noble truth is not about ordinary suffering only, but mostly about ageing, sickness and death (and rebirth! and lower realms!)
Scaping from Samsara by achieving Nibbana is also part of the noble truths... so if you think about it carefully you may see that: Yes, it is necessary to believe in those things to accept the Noble truths and without the Noble truths I cannot see how can one be a Buddhist (can be a nice person for sure, but not a followr of the Buddha)
Buddha said this verse in Dhammapada 176 to show the importance of it: "For a liar who has violated the one law (of truthfulness) who holds in scorn the hereafter, there is no evil that he cannot do."