So I have actually applied and received a B1 visa after filing for an I-130. I did this in Johannesburg and was also worried about the possible denial since I was obviously immigrating in the future. I'm not sure why the CO approved my application, but I was very upfront and honest with him during the interview. I also had proof of ties to a 3rd country, being back on my way to Thailand in May to wait out my I130, I had a contract for hire in hand and past work visas for Thailand in my passport (I applied for the B1 in March). I think the fact that both my wife and I being teachers played a role in the decision as you can't really teach without a EAD in the US so the risk vs reward of staying illegally on a B1 was low. At the time of writing, I am visiting the US for the second time this year, each time being granted 6 months stay and leaving after 1 month (leaving again tomorrow morning, sadly).
This long winded reply is just to say that it is possible to get a B1 visa while already processing an I130, but it is up to the CO in the end. I might have just gotten lucky.