Which is correct: I am concerned about whether there has been or have been any accidents.
The correct forms of your query are
I am concerned about whether there has been an accident.
I am concerned about whether there have been any accidents.
Both forms can mean the same thing since to ask about one accident (without specifying a specific accident or situation) is to ask about all accidents.
If you said
I'm asking about whether there was an accident.
Has there been an accident?
Was there an accident?
You might get the reply
Yes, there have been several.