It is not possible to record Saffire's internal DSP reverb to disk within any audio software. However, there is a good reason for this. Normally, it is not desirable to record reverb directly to disk. Usually, it is advantageous to record the signal dry, or with only dynamics processing (compressor) and equalisation (EQ). This allows for maximum flexibility during mixing. If you commit to a particular type of reverb on a vocal, and then decide later that you'd like less reverb, it's too late. However, if you want to apply reverb later, you can always use the VST or AudioUnit reverb plugin(s).
So, why have an internal DSP reverb if it can't be recorded? Well, this type of reverb is commonly called 'comfort reverb'. It is provided for headphone mixes, for vocalists and musicians who like to hear themselves in the headphones with reverb in order to lay down a good take.