Just like you can't directly contribute to Gnome without using gitlab.gnome.org, you can't directly contribute to Lemmy without GitHub.
Or rather, easily. If you're submitting something simple, you could communicate with Lemmy Devs over Matrix and ask if they're amenable to receiving a git patch they can create the PR for. https://join-lemmy.org/docs/contributors/01-overview.html
The thing about morality is that it is subjective (granted there is some discourse on that whole topic).
Whether it is immoral - there are societal groups that would consider it immoral. There are also ones who wouldn't find anything wrong with it.
IMO, what ultimately matters is your own morality, and past that, how those you care about would view it (their morality).
Harmful is a whole other topic with a lot of facets though. That I can't help with.