I don't think you'd see much benefit (in terms of added nitrogen) for single season crops such as peppers and tomatoes. Legumes are great nitrogen fixing cover crops. But my understanding is that the benefit to the soil is provided when they are plowed under - not when they are actively growing. Within the confines of a container, I think you'd be creating nutrient competition.

What makes you think you need the extra N - that's what fertilizers are for. ;-) Even if it was to add N, it would be competing for everything else ...... and how are you going to deal with THAT?

I'd skip the idea, depend on your fertilizer as the N source, and mulch with bark or similar if you think it's necessary. Keep in mind that you can't turn over a cover crop in container culture like you can in the garden. There are a lot of significant differences between container culture and gardening, one of which you probably just hit on.

Best luck to you!

Al