I would say that it would be a bad idea. It would smother some of the early flowers, would not look nice and would encourage milldew. A beautiful shrub standing on its own.

How about an annual? A few Canary Creeper for example.

What about under planting with something small, bright and spreading, like small campanula for the season after it finishes flowering?

Thanks for the ideas. The viburnum is about 8' tall, more like a small tree and it has finished flowering by April. I'll google canary Creeper. I do have two varieties of Campanula already.

I have a summer flowering clematis in mine which is about the same height as yours. It is planted quite a bit away from the tree root ball.

Thankyou Jen. I was hoping a honeysuckle or clematis might be ok.

Something like clematis x cartmannii 'Joe', which only reaches about six feet, would not overwhelm the viburnum

Thanks Andrew, I'll check that one out and see if I can buy one online. The canary creeper looks lovely but they say it's tricky to grow and having little confidence in my gardening skills, I decided to go for something I can plant rather than grow from seed.

The clematis I have is Clematis 'Comtesse de Bouchaud'
it brightens the whole shrub/tree in the summer.
http://www.clematis.hull.ac.uk/new-clemdetail.cfm?dbkey=130