The SmartDrive 2002 doesn't prevent it: it depends on your computer case: if the 5-1/4 drive bay mounting screw slots are long enough that you can pull a CD drive into a recessed position you should be able to do the same with the SmartDrive.
But there are some small air slots in the side- and upper-edges of the SmartDrive front panel to enable air to flow in along the sides and top of the SmartDrive enclosure. So if you shut off the flow of air from the front, the SmartDrive will not have as much cooling airflow.
Smart Drive 2002
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I've had a Raptor 150 in one for several months, and I haven't observed overheating (but have not taken a scientific measurement). But there should be some airflow over the smartdrive -- there's more likelihood of overheating if the smardrive is placed out of the airflow and depending only on convection. (I.e., the speed of your fans is not the issue, it is a matter of whether your case makes the air flow past the smartdrive when you install it.)
You don't really need any airflow with the Smartdrive 2002c enclosure when using a standard 7200rpm hard drive. 
It works happily as an external enclosure sitting outside the case. If anything it works better as an external enclosure than mounted within the case.
I originally had my main Samsung Spinpoint T 400gb drive in a Smartdrive 2002c enclosure directly underneath the DVD drive in a 5.25" bay. The hard drive temperatures were fine but I had two DVD drives die in quick succession shortly after buying the enclosure.
Possibly it was a result of the heat from the hard drive.
Mounted on a block of foam it's very easy to just push the enclosure back into the case and fit a blanking plate in front if needed. I had my one without a blanking plate in the hope of a little more airflow around the enclosure.
Smartdrive 2002c enclosure in Antec Solo Case
After that it now sits outside the case on a block of foam. Hard drive temperatures are better than they were in the case and it's no louder than having it in a 5.25" bay.
External Smartdrive 2002c enclosure
Have a look at Oscar3d's PC also where he has three hard drives in the same layout:
viewtopic.php?t=44219
The actual enclosure transfers quite a lot of vibration. If you have it hard mounted to the case it's almost as bad as having the hard drive by itself.
If you can get it isolated from the case it does work a lot better though.
You could consider an alleycat enclosure too.
viewtopic.php?t=20305&highlight=coolpack
It works happily as an external enclosure sitting outside the case. If anything it works better as an external enclosure than mounted within the case.
I originally had my main Samsung Spinpoint T 400gb drive in a Smartdrive 2002c enclosure directly underneath the DVD drive in a 5.25" bay. The hard drive temperatures were fine but I had two DVD drives die in quick succession shortly after buying the enclosure.
Possibly it was a result of the heat from the hard drive.Mounted on a block of foam it's very easy to just push the enclosure back into the case and fit a blanking plate in front if needed. I had my one without a blanking plate in the hope of a little more airflow around the enclosure.
Smartdrive 2002c enclosure in Antec Solo Case
After that it now sits outside the case on a block of foam. Hard drive temperatures are better than they were in the case and it's no louder than having it in a 5.25" bay.
External Smartdrive 2002c enclosure
Have a look at Oscar3d's PC also where he has three hard drives in the same layout:
viewtopic.php?t=44219
The actual enclosure transfers quite a lot of vibration. If you have it hard mounted to the case it's almost as bad as having the hard drive by itself.
If you can get it isolated from the case it does work a lot better though.
You could consider an alleycat enclosure too.
viewtopic.php?t=20305&highlight=coolpack