Align 3D After Effects items with 3D render

I'm not entirely sure what this would be called, or if I'm doing the right process and I'm just not good at it.

After I animate something in 3D (currently using Luxology Modo 601) and then I render out the flat PNG image sequences, there's certain 3D elements I'll animated alongside in After Effects. So, if I animate a camera panning past buildings in 3D, but the trees in the background are 2D (3D items in After Effects) and I try to make them align/map properly.

First off, I don't know what that's actually called, just compositing 2D and 3D elements? More importantly, it's complete guesswork trying to make a 2D item try and fit in with a 3D render, and I'm just going along trying to match it by guessing with Orientation/Position/Rotation.

So, lets say I render out a 3D rotating building, and I want like a 2D logo rotating around it the same (but the 3D on the logo has been done in After Effects, not Modo) is there a simpler way to do this? Is it guesswork, lots of time?

Similar to this video https://vimeo.com/27194571 (around 3-4 seconds in), there is a magazine spinning, and 2D elements around it. The 2D elements feel like they've been matched right with the magazine, but done in AfterEffects. Again, I'm wondering if there's a name for this or what not.

*I've read CreativeCow forums for years, but brand new member as of today, so I apologize if I've posted this in the wrong location.

Perfect, thanks so much for the response. I'm trying out both options, really appreciate it!

Alright, so just tried it with two different files, and it works pretty darn well. The only issue I had with it (and it could entirely be from me being a noob and not adjusting something proportionately) was getting the 2D item to be in same 3D position as the null object I exported from Modo. The item is aligne perfectly to the camera, but I had to mess around with the anchor point to get it to line up. Otherwise, it couldn't be simpler, and the guy has a video that walks right through the whole process.

In modo, it was giving me an error that the film back didn't match the frame size. Was simple enough to adjust (by changing the Film Back setting in Modo). I'm assuming you can get it to work with any frame size, but I'm not sure if me using a non-standard video size (it was like 1344x732 or something odd) was causing that to happen. I switched it to 720x480 frame and it went through fine.

I didn't get a chance to try out and 3D trackers, but after work I'll give that a shot too.