If you make such a request at 180 out, it's no problem. Otherwise, for a request for 6 during a busy week, you may have much better luck asking them to check what is available, then make your restaurant selection.
Can they check? Yes. It's my understanding they check once a day. Personally, if I was going that route I'd check myself multiple times a day.
I spend a decent amount of time checking the restaurant board. Frankly, I've been amazed at the number of folks who book multiple reservations on the same day. (And I'm talking more than 4....) Sometimes they are at the same restaurant, or within an hour of each other.
How do I know? They post their cancellations.
Here's the link to the Nov. Cancellation board. Check post #1 for details on how to use the thread if you haven't before.
http://www.disboards.com/showthread.php?t=3336585
Another good strategy is to use the phone app. It's easy to check frequently, and I'd recommend that. As your trip gets closer, especially at the two week and one week mark, people seem to firm up their plans. Popular restaurant reservations seem to spring up then, even for groups of 6 or 8.
Hope these tips help. I use the IPO for some things, but for hard to find restaurant reservations after 180+, I work on them myself. I see how fast they pop up and disappear. Chances aren't good that only once a day checking from the IPO will get me a hard to get reservation. They come and go quickly!