Hi Rahul
So it seems like the main clock speed of the Diecimila is 16MHz. The ADuM3150 can support up to 17MHz SPI communication without the delayed clock mode. This means that the performance of your SPI system wont be improved by using the delayed clock operation.
If you still wanted to implement this feature on the Arduino I'm not sure if this particular model will be able to handle this operation by itself. You could possible have an external shift register collect the MISO data with the dlyclk then the microcontroller read from it.
Joe