That would be fine but you could give some context with that initial approach so that the other person can decide if they can stop or not.

i.e. "Are you busy? Could you help me with blah blah"

If you're getting bombarded with "you there?" from 20 people because some service they use has gone and right now you're trying to fix it for them all, well that can be stressful too.

If you just "Hi." with nothing else they might never know to get back to you on a completely different issue.