Yeah, technically it requires diacritical marks, but unlike French they are only written explicitly when they fall on the final letter of a word. Italian only has seven vowels, so these are the only common ones: è é ì ó ò ù à.
What I would do is this:
- Replace them with a single quote -> E' instead of È or É and so on.
- Ignore all uncommon marks.
In most contexts, it is perfectly acceptable to do that. A native speaker would understand without giving it a second thought or considering it impolite. I write emails to my boss like that.
If I had to make something meant for the public (say a UI, or a document), then I'd switch to the Italian layout for that purpose only and then go back to the US one.