Yes, the crocus would be past bloom once the roses leaf out, but I do wonder if the foliage of the crocus would have time to mature enough to rebuild the bulb for next year or will the foliage of the roses interfere? My suggestion would be to try a few crocuses along the edge of the rose plantings as they should get the best conditions there and the most light. Later on you could divide and replant the corms in between the roses.
Crocus tommasinianus is the toughest little crocus I know. It blooms really early, it has small demands on nutrition and naturalizes well. It divides freely, yet it can be left in the same spot for a decade without replanting and still bloom. Really a great crocus and worth trying.
