In this sentence, I would add a comma after ‘DJ.’ This is because the phrase ‘including a DJ’ is a reduced relative clause and not a necessary part of the complete sentence. In full, this clause might read: ‘which were including a DJ.’ However, you will rarely see/hear people use a complete clause in an example like this.
So, if we remove ‘including a DJ,’ what do you think the correct answer is:
‘Two personshas/havebeen arrested in this connection’?
So. to generalise can we say that when two or more subjects are joined by ‘including’, the verb is used according to the first subject? I found this particular sentence the other day when I was going through “The Times Of India”(it’s a popular newspaper in India). In there they have used the singular verb ‘has’. That’s why it was creating a lot of confusion. But now that you have cleared my doubts, it is gonna be alright.
In this sentence, the complete subject is: ‘Two persons, including a DJ.’ However, ’Two persons’ controls this subject. The phrase ‘including a DJ’ modifies ‘Two persons,’ and it is a non-essential phrase. Therefore, the verb only agrees with ‘Two persons.’
To be honest, I would write this information a little differently because I use US English. I would write: “Two people, including a DJ, have been arrested in connection with this.”
Keep in mind that there are different forms of English in India as well. These forms of English do not always follow the same grammar as US or UK English, but they are usually more similar to UK English.