As I understand it, it's basically the result of a kernel driver (the Wolfson audio add-on driver) that is 'reserving' that I2C address. It can safely be ignored, just don't try and put your own device at that address. This thread has instructions for removing the driver modules if you really want to.
Which doesn't explain why your DS1624 is not showing up. Make sure you've pulled all the address select lines high or low; don't leave them floating.
Check the datasheet. It shows an operating voltage range of 2.7V - 5.5V, so it should be fine with 3.3V. It has three address select pins, A0-A2. Connect them all to ground. That should show up in i2cdetect at address 0x48