I've had a spoke break on my rear wheel and catch the RD, locking up the wheel instantly. Luckily for me all it did was bend the hanger a bit. I don't know if it was a single-spoke failure that got worse when it caught the RD, or if multiple spokes failed at once - I was right at the final max effort part of an uphill sprint interval when it happened so there was definitely enough stress on the wheel if one spoke went a bunch more could follow instantly. I had several broken spokes and a bunch of bent ones when all was said and done.
So I could see a case where a broken front spoke could cause a front-wheel lockup if it were to come loose in a way to allow it to catch the fork.