I put artemisia 'Powis Castle' at the base of one of my purple-leaf sandcherries just as an experiment last summer and the one that had the artemisia around it didn't get eaten like the others. BUT - I don't know for sure that Japanese Beetles were the guilty bugs and it could've just been a coincidence. I have a few crape myrtles and only one of them gets lots of Japanese Beetles while they leave the others alone (so far) even though some are the same variety. They haven't been bothering my roses either (yet).
Something to consider - You could hand-pick the beetles off your roses unless you have too many but the crabapples and grape arbor would be too tall.

My original experience with JB was a small mixed perennial/wildflower garden in front of my last house with a border of spruce. I had three favorite hybrid tea roses in there because I just couldn't resist them--French Lace, Angel Face and Mr. Lincoln. I would dust them with pyrethrum every once in awhile. Well midsummer I got really, really busy for a week or so, and then one weekend went out to check my garden, and thought . . hmm? where are my roses?! I was heartbroken and blamed myself for being a bad mother. I don't want to go through that experience again. Were my roses sacraficial lambs? Nothing else was bothered. Or were they just stressed anyway, by the spruce needles, and that made them vulnerable?

How about milky spore in the ground? Then you shouldn't have much of a problem.

Loooooove that pyrethrum it's natural and works like a charm ; ).......