You can please yourself about the correct way to cook frozen sausages ginejbee, but I can assure you that chip shops just dump frozen sausages into the chip frier just like they do chips and I have never come across anyone who has succumbed to food poisoning using this method. In fact, the Federation of Fish Friers recommend the method.
It's nothing to do with the oil temperature. Sausages cook evenly and distinctively in chip shop friers regardless of the fat type, time and temperature involved. If they are cooked externally evenly,they are done.
Do you really consider that chip shops should defrost frozen sausages before cooking? Chip shops don't use chilled sausages. Having worked in a chip shop in my student days, I can assure you they'd soon be out of pocket if they defrosted frozen as you propose. Chip shop frozen sausages are no diifferent to the frozen sausages you buy in a supermarket.
If you really wish to waste your time and electricity in defrosting sausages before cooking in your microwave, it's your decision. I suggest you discuss the issue with your nearest chip shop proprieter. You never know, you may find your electricity bill decreases.