Do I have to beat Red before catching Groudon on Pokemon Soul Silver?
Yes. You have to beat Red then go to Mr. Pokemon (The one that gave you the pokedex, above Cherrygrove Town) to get a red orb. Then you need to find the hidden cave/pathway on route 47. The first cave with the hiker is the entrance, go downstairs and surf left all the way until you meet some rocks, pass them and continue left, then go north and use rock climb until you reach the cave/tower where you have a battle with Groudon. Haha hope I’m not too confusing.