This question is not about a Barlow lens.
Yes! Those with a Coudé focus and others
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show and link to a wide variety of reflecting telescope optical designs that include negative focal length mirrors and off-axis deflection. (Check them out, but two examples are shown below).
As for a proper, classical Newtonian with its truly 45° diagonal, it will certainly have been tried by some amateur, somewhere, sometime, if for no other reason than they didn't have access to a primary mirror (blank, or figured) with a hole in the center.
Another reason would be viewing convenience - that side-viewing option is pretty handy when your DIY portable telescope is big and heavy and for mechanical reasons a tall mount high enough to make bottom viewing with an external diagonal (inverting or fancy non-inverting) a pain.
Just for example, LOptics.com's Building an open-tubed 12.5" F/12.5 Classical Cassegrain By Michael E. Lockwood