Well I vote for a mix, and I wouldn't recommend putting grasses in the middle and roses on the ends. I would suggest mixing them in a more naturalistic way. Several reasons for this. Several different plant varieties (biodiversity) will be more interesting, more wildlife friendly, less likely to get a disease or pest to take the whole hedge out, and more seasons to have something of interest. Roses (depending on kind you get) are mostly a spring thing, or summer and fall. Usually nothing going on in winter. The grasses are typically cut back in late winter/early spring, so they are pretty in summer, fall, winter but not spring. I would recommend a variety of grasses, even 2 different kinds, a different color or texture. I really love the knockout roses, I have many roses including old garden roses, and knockouts definitely perform the best, are carefree, and bloom alot. I think the red ones perform the best. (I also have pink and yellow). Have fun with your new project!

festuca glauca makes a nice edging grass for such a border if planted in individual clumps. The bluish tone of the grass stands out against the nearby lawn and nicely against the dark greens of roses. Pull the blooming parts(seed heads) and the plant will do better.

I think I am leaning towards a mix of primarily ornamental grasses with a few rose bushes while throwing in a few small perennials/annuals for some more color. The grasses I am looking at so far are Miscanthus Morning light, Karl Forester's Feather reed, Miscanthus Adagio, Miscanthus Sarabande, fountain grass and festuca glauca.

I am now looking for rose bushes that fit the look and also the humidity/fungus issues with roses in central NC. This will take some research but so far I am definitely going to try Ducher somewhere. I like whites and yellows. I think I will eventually use a double red Knockout also.
So I have a lot of research on rose bushes to do in addition to starting the bed preparation process using some version of the Interbay Mulch/lasagna systems.
Any thoughts would be appreciated.

I really like the Antique Rose Emporium in Texas for rose info. You can easily find them online and then search all the different classes of roses, by size, color, fragrance etc. These old garden roses (OGRs) are disease resistant and most folks that grow them don't use pesticides nor fungicides and grow them in a shrub border. They also identify especially low maintenance shrub roses I think called Earthkind roses. I think you will find alot of good ideas there.

Do you have deer around? If so, they (and other critters--ground hogs) LOVE to eat roses--leaves, flowers... while any ornamental grass is COMPLETELY ignored (personal experience). Just thought I'd mention it in case animals are an issue.

15 years ago I planned and planted a lot of stuff in my backyard. Deer ate nearly everything the first year! They would even come up to my front door and pull pansies. I gave up.

Things have changed over the years and we don't seem to have as many deer (i.e. I don't just see them in the open like I used too, don't see their hoof prints in the yard, etc.). So I am going to try again. I do have one 5 year old Knockout rose that has been left alone. Good to hear about them not liking ornamental grass.
I am also going to spread Milorganite around. I have started using this for my lawn grass and it is great. Over the years I have read and been told that deer really hate this stuff. It is made of recycled sewage waste from Milwaukee WI. Great low dose fertilizer with iron.