Hi,
What kind of metadata do you have?
For the case that you deal with numerical metadata:
You could surely do this.
Another approach would be to repeat your Metadata until it has the same dimensions as your images and start feeding it into your Conv layers. This would have the benefit, that you do not have a mixture of abstract/learned features and “handcrafted” features/Metadata. Your network would learn to build abstract features out of your metadata as well.
However, your approach could work too.
In my opinion it is something like a philosophical decision.