I cannot see how having a dedicated sample drive, whether SSD or not, would cause most people to have problems with the programs finding the samples unless they were not installed correctly.
 
MOST people should (and likely are) be able to install samples onto a separate drive without the sampler having problems locating them.  the installation programs put registry entries in the OS registry telling the program where to look for the samples.
 
however, YMMV.  It may be dependant upon other factors in your system that we're not aware of, such as editing of the registry either manually or by an automatic registry cleaner which was not set up correctly causing deletion or modification of those entries needed by the program to find the correct location of the samples.  Or something completely different...

Worth mentioning because I'm not sure a lot of folks understand how it works. 
 
If your using per project folders like you should be, 
It don't matter where your project files are stored.  
I Keep some projects on C drive and most on my second E drive. 
There is the default path where Sonar goes when you go to the "open" dialog. 
You need to change this if you move your folders to a new drive or location or it will always return to the default. 
But you can browse to where ever you want and open. Until you close Sonar it will return to the place you were each time you use open. 
I think most importantly is the audio is streaming in and out of your fastest, cleanest drive. 
 
I sort of agree with Wayne, if your C drive is capable and you use your other drives for regular back ups you could get away with 1 big fast drive. 
I like to keep data separate in case C drive needs a re do.  

Beagle
I cannot see how having a dedicated sample drive, whether SSD or not, would cause most people to have problems with the programs finding the samples unless they were not installed correctly.
 
MOST people should (and likely are) be able to install samples onto a separate drive without the sampler having problems locating them.  the installation programs put registry entries in the OS registry telling the program where to look for the samples.
 
however, YMMV.  It may be dependant upon other factors in your system that we're not aware of, such as editing of the registry either manually or by an automatic registry cleaner which was not set up correctly causing deletion or modification of those entries needed by the program to find the correct location of the samples.  Or something completely different...

That's the problem, you have to be very careful on setting your samples and their programs just right. One wrong move and you'll have location issues that will drive you bonkers. I just find it easier to put everything on one drive and forget about it. Computers don't always act like they are supposed to. 

Level of expertise comes to mind.  If you're more comfortable putting everything on one hard drive, then please do so.
 
there are benefits to using more than one drive beyond what has been mentioned, such as simultaneous read/write on different drives which wouldn't be possible on one drive.  the OS and the program (Sonar) will be reading/writing to 1 drive while the audio streaming during recording/playback would be occurring on the other drive if set up that way.
 
with one drive, all of the read/write tasks would have to be shared between the OS, Sonar and the audio stream.

Aside from performance benefits, having separate drives for data storage will also relieve your system drive of some of the workload to save wear & tear and reduce the chance of drive failure.

There's a further advantage too.  It's very convenient when to come to migrate computers if the data that needs be copied (or moved) across is stored separately rather than mixed with ephemeral stuff.

Just sharing my experience. No need to get insulting. I don't have any issues with everything being on one drive. If you want to use multiple drives, go right ahead.