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As a leaf wash, yes. Rose foliage picks up a surprising amount of grime, particularly in a town garden, near a road or under overhanging trees, and the glossy-leaved varieties show it first. A weak neem wash, misted on and wiped or left to dry, takes the dust off and leaves the leaves with a soft sheen. This page covers how to do it on a rose; the recipe itself is on our leaf-shine spray page.
Which mix
Start light: one part water-soluble neem to a hundred parts of tepid water, or 5 ml of pure neem oil with 1 to 2 ml of liquid soap in a litre of warm water, shaken to a milky blend. The richer one-in-ten mix is for old, leathery leaves on an established shrub; new spring growth is soft and does better with the light wash.
When
Morning or evening, never in strong midday sun, and on a still day so the spray lands where you point it. Leave a fortnight or so between washes. Freshly planted roses can wait until they have settled in.
How
Mist lightly over the top and underside of the leaves; the undersides collect as much dust as the tops. Wipe the larger leaves with a soft cloth if you want a cleaner finish, or leave the wash to dry. Keep it off open blooms and buds, because droplets can mark the petals, and on a variety you have not washed before, do a single stem first and look at it the next day.
Mix fresh
Make what you will use in one session and use it within 48 hours. Neem oil sets when it is cool, so on a chilly morning warm the bottle in a bowl of warm water before you measure, and use warm water in the sprayer so the mix stays milky. The earthy smell fades as the leaves dry.
Rose foliage is only part of the picture, of course. Neem cake, the pressed seed meal left after the oil is extracted, is used as a slow organic feed around roses through the growing season; there is more on our neem cake page.