Iteration vs Recursion question in Lisp method
Since deep-reverse and iter call each other, they are (mutually) recursive.
Their combination is not tail recursive however, so deep-reverse is not iterative in the scheme parlance (IOW, does not admit tail call optimization).

PS. A proverbial sufficiently smart compiler (and, in fact, many real ones) can compile this function into an iteration (i.e., not using the function call stack).