Guidelines for running tv cables behind walls for an HD TV
The placement of the hole is not critical so long as it will be behind the tv panel. Obviously a hole immediately under a structural component of the mount might be a problem. 

The mount is more critical than the hole. Buy the type of mount you need and see where it lands in relation to the hole. There may be no conflict. If there is, covering the old hole and making a new one is not hard. 

A bigger issue is how you terminate the wires and cables.  Are you bringing power to an outlet immediately behind the tv? If so, you need an appropriately mounted electrical outlet box. Additionally, a hole may slightly compromise insulation and allow a draft, so it is a good idea to have a box and a cover plate for the cables even if the are not power cables. 

There are specialty outlet boxes with low voltage media connectors or access holes. You should determine the placement of this after the mount is in place on the wall.