That's an interesting idea, replace the burners in a scam jet with a electo-magnetic plasma doohickey. Basically an electric ram-jet.

Edit: My dad mentioned in school doing some scut work for a group designing an external combustion engine. Use the shock waves off the body to compress air, add fuel, zoom. Not sure if you could make that work with with an external heat source.

Side note: My understanding why people want to use hydrogen is it's a light particle, making it easy to accelerate it to high speeds. The higher exhaust velocity the better the ratio of payload to fuel becomes.