I think they could enjoy it, depending on what you have planned for him. My kids are pretty much convinced this year that Santa is a myth but they still are looking forward to Elvin. Elvin brings them a new Lego Advent Calendar on Dec 1 and new personal ornaments for the tree on Dec 6 (if they have been good). Around the 15th he has a note from Santa about where they are on the Naughty or Nice list & what they might want to do to improve their standings. If they have been really good he might show up with a small gift certificate from Target or Game Stop on Dec 21. If I am feeling energetic he arranges a scavenger hunt that ends with a promise of going out for breakfast one weekend morning. Plus the usual things he gets into - dying the milk green, scattering their socks & underwear all over their beds (I have no idea why but they find that hilarious), creating his own Mii and playing Mario Kart all night, etc.
They like these things & a belief in Santa isn't entirely necessary. It's a little surprise every morning that makes the month special. But I never played up the 'reports to Santa every night' thing. It made my youngest not like & be afraid of Elvin. He would get terribly upset for accidentally spilling milk out of fear Elvin would tell Santa he was bad & he wouldn't get any presents. So Elvin goes back to the North Pole every night to check in with Santa & make sure all the toy production is going well and to chat with the other elves about the families they are with so he can get ideas of things to do with us. If the boys have been really bad - fighting, name calling - yeah he'll tell Santa about it, but mostly he is with us to help remind the boys to be generous to others & one another every day.