It isn't that Perry is the same guy or not - it's that he is a down lineman with different responsibilities that allows for Neal to be on the field on that side, and Matthews in the middle. That alignment will be more stout against the run, and provide many more rush options if it is a pass - plus, you can run/blitz more easily out of that.
If Perry is an OLB, Matthews can still line up in the middle, but then you'll have Barrington on the field, no?? Barrington stepped up his game a great deal last year, but he is still a 4.92, 40 guy, and always will be. Marshawn Lynch leaving him in the dust for an easy 30 yd gain when the wheels started coming off in the NFCC Game should be a lasting reminder of why you don't want Barrington in the nickel.