Buddhism comes from India, where Uddiyana was a major crossroads where a lot of high level hindu tantra philosophy and buddhist philosophy arose together. They are very intimately connected, with some (major) deviations on their personal philosophy. In particular is the identification of the highest tattvas in Shaiva & Shakta philosophy with the transcendental-i, whereas in Buddhism it's conceptually an external All-Buddha rather than your own self... yet also your own self since it's the essential force? Sort of tricky. For the actual sadhanas though, they are very similar in praxis! You'll find, however, that the framing ritual for every tibetan buddhist sadhana will follow principles of the three jewels, the seven line prayer, etc which are not present (and maybe not totally necessary) in hindu tantra sadhanas for the same deities.
Christopher Wallis's Tantra Illuminated goes over these differences from an academic context. I believe some of his final chapters on surviving lineages of Saiva philosophy touches on Dzogchen concepts being very similar. There is another book that does the same, but its name is escaping me right now...