Personally I think that this is a good option if you can find a good bank that will give you a good amount of money and make sure that you have the right deal for this. I only worry about it because you are leveraging the whole property so as far as the risk scale goes it is high up on the scale. I got quoted for a 95% LTV at ~5% interest that had interest only payments. So basically you need to roll those numbers into the price of the repair to really analyze the deal.
For example, If you get a $50,000 HELOC and you are using that for the purchase and add it the payments to your carrying cost it can work. However, what happens if you go over budget and cannot refi out all of your money, are you still ok have to pay the HELOC down on your current income. It can be a great tool to get access to quick cash, especially if you did value adds to your residence...
My understanding is that you then have basically purchased the property with cash and therefor you do not need to season the property (i.e. get renters in) once the rehab is finished before pulling out fix debt on the property (obviously credit score and debt to income can be issues here).