If you had a larger tank, then you might be able to mix the species but in a 20g you will be maxed out with just one of these animals. And no, they don't like others of their own kind very well......
The biggest difference besides markings between the two eels is size. The tire track (which I think is better looking JMO) will get to be "about" 25" and the peacock "about" 15" or so. Before anyone gets the wrong idea, these animals are rather slow growing. In other words they won't reach their maximum length in a year or two. And also, even though they are long, their bodies are thin (compaired to their length) and very supple.
Other points; these fish will appreciate a hiding spot. A piece of PVC pipe will do nicely. No plants other than ones that can be attached to driftwood, rocks, etc...java fern and anubias will work. All other plants will be uprooted. And don't forget, eels are notorious escape artists. ALL openings must have a tight cover. You can also lower the water level in the tank slightly to help keep the eel in.
HTH