He was our ally as well. I had the players meet him in Vallaki, but he kept his disguise. he DID tell them some lore about the valley, and interpreted some of their other card results, using the guise of a "travelling collector of stories, this is stuff I've picked up along the way and by exploring Barovia myself." later, when the group got into some shenanigans and had to make a quick exit from town, he assisted them, and told them "Find the Tome of Strahd (he'd previously interpreted the clue as to where it was for them) and meet me in two days at the old tower on Lake Balinok. I'll tell you more then." After they went and retrieved it from the Abbey and met him there, he invited them into the Tower, and basically told them (in lots more words): "You've shown me trust by bringing this item here, I'll return that trust now. Rictavio is a disguise I use, my name is actually (spoiler). I am a student and hunter of monsters. I have been studying Strahd for many years, and felt the time has been drawing close to confront him. With you here now, fate has brought the pieces into place. Gather the other two artifacts, meet me back here, and we will finish this together."
Until that point, the players had just been moving from quest to quest around the valley. This episode helped direct them, focus their attention, and will drive the story to its conclusion. They've since retrieved the sword, and know where the holy symbol is but need to find a way to get it from it's keeper. And then, it's off to the Castle!
The trick with Rictavio is not using him as a Mary-Sue. He is the Sage, the Yoda-character, and very powerful - but you have to be careful not to let him take over your plot. The PC's still need the autonomy to make their own decisions. Rictavio can give them information, guide them and make suggestions, but shouldn't just tell them what to do. Also, he knows a lot, but not everything - he should be a bit of an unreliable narrator. Otherwise he'll just turn into the campaign "Wiki" for the players, which you don't want. I'd suggest not having him join the party, unless they need the extra healing he can provide. He can be off doing other things while they are doing their quests, and therefor available only when you want him to be. This again keeps the player's reliance on him to a minimum, while still allowing him to be useful when he's needed.
Hope that helps!
