I've heard of softbank before, but only in passing. I'm not aware of any scandals they've been involved in. I suspect this is only a money deal, and at least while ARM continues to innovate and make money, softbank won't be exerting any pressure for change (and if ARM does make a misstep in the future, softbank is as likely to just sell up, I think, rather than trying to run anything from Tokyo).
Edit: It turns out ARM is going to be delisted from the stock exchange, so softbank can't just sell up through the market. They're not a majority shareholder now, they're a private owner. They could relist it, but if it's already failing by then that might be difficult.
Herman Hauser's quite concerned about ARM being run from Japan from now on, but I'm not sure I've ever really trusted that man's judgement on anything much. However, softbank is funding extra engineers for Cambridge, so it's not a completely hands-off operation.