The spec sheet shows the total width of the sink, including flanges, to be 29". A 30" cabinet is the exterior dimension- the interior width is less - my 30" cab is 28.5 inches on the interior. You would have to go measure the inside width of the Ikea cabinet to see if it would be more or less. The bowl of the Kohler is 27.5" wide, so it will fit with 1/2 inch to spare on either side if the cabinet interior is at least 28.5".

The modification that they are mentioning, I assume, is to cut down the sides of the cabinet a bit to allow the sink flanges to actually fit between the side and the counter.

People successfully do that, although I don't know if Ikea cabinet construction is different in anyway to make it not possible. The disadvantage would be that the counter would have to be pulled if you ever need to replace the sink.

It seems, from what I've read here, that cutting the side down a bit isn't a strength issue especially if you have another cabinet up against it.

That sink will fit in a 30" cabinet without modifying the cabinet. You'll undermount it with a front and rear Sink Strap from Regent Stone Products.