According to the link you've provided, the coil draws very little current, and the person posting that comment suggests that it can be directly driven by an arduino. I would hesitate to use more than one to a board without additional research in that respect.
The comment also suggests that a capacitor be placed across the coil terminals, which will also protect your circuit from excessive power draw causing drop outs.
The research I've done indicates that the digital pins can handle a maximum of 40 ma, but the recommendation is no more than 20 ma, which is lower than the specs for this relay.
If you are going to use more than one on a given arduino board, a shift register or equivalent would protect your board and give you reliable results. For a single relay, consider this resource:
Some additional research may lead one to believe that even 20 ma is too much current to draw, so the transistor option is certainly the safer route.
Be certain to use pull-up or pull-down resistors, depending on your configuration with the digital pin selected.
You didn't indicate what you were going to be connecting to the N/O or N/C pins, but that won't matter if they are external to the arduino and do not exceed the specifications of the relay.