Typically a Ramjet, is defined the other way around. Carry and provide the fuel, but use the oxidizer from the atmosphere. I.e. Ram in the oxygen to get the density sufficient, and combust it with fuel you carried along.

Nonetheless, it is not very realistic for orbital operations, since on an orbital flight you want to go almost straight up to get out of most of the atmosphere as soon as possible, then tip over once clear, and accelerate to orbital velocity.

Thus your time spent in the atmosphere with sufficient oxygen to use as it flows by is minimized. If you want to change that and accelerate to orbital speeds within the atmosphere, you run into heating issues, as you might imagine, and drag issues that usually are considered enough to make this an unsuccessful approach.

For missiles and things that stay in the atmosphere, it seems like an interesting idea though.

Science fiction has dealt with this type of engine quite a bit. So far, it's still science fiction. There is such a small amount of hydrogen that you have to be going very, VERY fast and have a huge scoop to get enough hydrogen to keep things going. It's certainly not something I would expect to see in the next thirty years, or even the next fifty. I'm not an engineer, nor do I play one on TV. I would just be very surprised to see a drive like this developed any time soon.