Yes, but you must have:
1: a HeartGold copy
2: Pokemon Dream Radar on your 3ds
and you must have gotten landorus in dream radar.
I'm playing through Dream Radar right now actually . So what you need to do is, after you catch Landorus, put your Heartgold in the 3ds. Click start on the home screen for dream radar, and the professor will show you a special extension where you can catch ho-oh in.
Sources: Knowledge and this http://bulbapedia.bulbagarden.net/wiki/Pokémon_Dream_Radar#Extensions
Also, the dream radar is 3 dollars in the e shop.