Is pragmatic truth inherently less valid than other forms of truth? If a Hindu
This is a complicated matter. Realist views of truth, including versions of the correspondence theory, hold that reality cannot or should not be split into different venues in which, say, Vishnu exists and is divine for one person, but not for another. Realists, then, hold that if Allah exists, then it is false to claim that Allah does not exist. The term "pragmatic truth" is a little puzzling to me, but perhaps what you are getting at is the idea that matters of what we call "truth" may be treated in terms of justification. So, for Saladon to claim that there is no God but Allah and Mohammad is his prophet, is to claim that he is justified in making such a claim. I suggest, though, that such justification or epistemic theories of truth are themselves pretty hard to justify (and, hence, on its own assumptions, a justification theory of truth might not be true because it is not justified).
There may be one other angle to consider. Some apparent disagreements may not be radical. Consider a dispute in which one person claims that The Morning Star exists, but not The Evening Star. And her friend believes the opposite. Fortunately, they may both not be too far apart, because it turns out that what "The Morning Star" picks out or refers to is the same thing that is picked out or referred to by "The Evening Star": the planet Venus. So, to go back to your example, there might be room to debate whether what the Hindu believes is "Vishnu" might be the same reality that the Muslim believes is Allah. For a philosopher who explored and defended this position, see the work of John Hick.