Sounds like the CAD Block needs to be exploded first.
Here's my method:
Place the sink into a blank plan, it'll yell that it's supposed to be placed in a cabinet, accept it and place it as a standalone object.
Go to CAD, CAD Block Management, find the symbol - it'll be the only one with a red +, select and press the "Insert" button.
Click to place the CAD block somewhere, then select it.
In the Edit Toolbar at the bottom press "Explode Block" - now you can select the outermost edge polyline.
In the Edit Toolbar again, press Convert Polyline. In the dialog, choose Countertop and press OK.
Specification will open automatically. Check "Hole in Countertop" and press OK.
Reselect all the CAD, press Make CAD Block in the Edit Toolbar, hit Open and give it a good name.
In the Library, right-click the sink and choose Open Symbol.
On the 2D Block tab, select the new block name you just made and press OK.
Now it should place into a countertop with a hole the exact shape of the sink.
Revolve Object is an interesting tool. The key thing is that it operates off the Selected Edge, and circles don't really have one, or, maybe more correctly they ONLY have one, so they're ... finicky.
Try drawing a Circle in an Elevation View, then using the Convert Curve To Polyline tool to break the circle into a series of smaller edges.
Then convert to a 3D Solid.
This allows a specific edge to be selected in order to revolve around.
I added +1 to the Rotate About X axis in this example to get a nice outward curve (rotating a full 90 at that exact edge tends to allow surfaces to merge and, well it's not a very realistic bend anyway.)