Not a Geophagus. . . would be cool if it was a Geo Taeniopareius, but, it's not, get a clearer pic up and you will certainly see that it is Heckelii. Please take note of the black first few hard rays of the dorsal fin. . . I bet that the back of the dorsal fin is starting to grow more than one extended ray from it as well. They can be aggressive, he/she will probably become boss of the tank quickly, but, won't necessarily do any damage to the others in the tank, but, you have discus, pretty delicate - I wouldn't risk it myself, even a true Geo would be pretty rough with discus IMHO. They grow into real beauties!
Good luck on what ever your decision, look forward to seeing the progress of the tank!