Answer: This might work for you as long as you allow space so the plants are not overly crowded as they mature. You would also need to be able to walk through them to reach the roses for their maintenance needs. Junipers do not really handle foot traffic, it tends to break their branches. They would also take years to cover the area so you would have weeds in the meantime.
It is more customary to use perennials around roses, partly because they would receive similar care: a pruning in the spring, some fertilizer in early spring and early summer, a steady layer of two to three inches of organic mulch. Some often used perennials that like well drained soil and full sun (as do roses and for that matter junipers) would be Nepeta, Dianthus, Thymus, and Salvia. The mulch also helps keep down weeds.
I hope this helps.
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