Aristotle and Longinus are similar in that they both recognize the inspired operation of the poet's mind and language. Plato opposes these views and considers poets and poetry inferior and potentially inferior.
One distinguishing aspect of Longinus' views is that he asserts that the poet's inspiration is a "fine madness." In other words, he expresses the view that poetic language and ideas come from an inclination to irrationality and distorted vision, a view that the finest poetry may make unseemly to hold.
One distinguishing aspect of Plato's views is that he asserts poets ought to be banned from society. He asserts that in his utopia, poets would not be permitted residence. In a way, Longinus and Plato do have mildly sympathetic impulses toward poets in that they both think poetry the product of peculiar types of minds, though that is as far as any similarity extends.
Nor in my opinion would so many fair flowers of imagery have bloomed among the philosophical dogmas of Plato, nor would he have risen so often to the language and topics of poetry, (Longinus, On the Sublime)
On distinguishing aspect of Aristotle's views, views Western civilization has followed and immortalized, is that poets are the bearers of divine truths that can known only through divine inspiration. This puts Aristotle at direct odds with Plato and somewhat at odds with Longinus. Aristotle asserts that the mission of poets is a divine one by which humans are taught lessons about life's great concepts by poetic inspiration that imitates divinity. During the Renaissance, Edmund Spenser, Philip Sidney and Shakespeare manifested this view in their own works.