Squamish language uses <7> conventionally to substitute for IPA <ʔ>, and I can imagine other languages doing so if their Romanisation was influenced by linguists. Squamish doesn’t use <!>, which turns up in Khoisan languages for clicks (Exclamation mark). Not convinced there’s a language that uses both, but who knows…
For the same reason of practicality, <8> substitutes in Wyandot language for <ȣ>: Ou (ligature).