Is it O.K. to plant flowers in pots that do not have a drain hole at the bottom?
You can get away with it if you put some aquarium charcoal in the layer of drainage gravel at the bottom and are very careful not to overwater. Having said that, it's better to have a drainage hole. Just put a plastic pot inside if you have some nice container you want to use.
Another thing you can do is drill a hole in it. I have done it with pretty dishes I have found at rummage sales and resale shops. I did not have luck with glass ones, but anything ceramic works good. Just start with a small tough bit.