I'm using Studio 8.5 and, for the first time, have been asked to record drum tracks with a Roland electronic kit. What do I need to know? Help!

Monitor the brain and record the midi output. On most systems if you try and trigger and monitor a VST  drum soft synth you'll be getting latency. And even a few ms is too much for drums. 
So patch the audio output into your monitoring set up but you don't need to record it. 
You can now easily edit the performance. You now have the option of using the perfected MIDI track to trigger sounds from either the brain or any VST or a combination of both for you finished audio track.
 

What Cactus said. Record the MIDI output, not the audio.
 
Later, you can use the drum kit's own sound module to render to audio if you like, but chances are you have better drum samples on disk and may elect to substitute some or all of the drum sounds with other sources. 
 
The audio output from the drums' own "brain" (why do they call the sound module a "brain"? Isn't the drummer the brain?) is going to be stereo, so you'd be stuck with whatever mix the drummer made. If the bass drum needs to be louder, or the hi-hats are too loud, or the toms are panned too wide, there'll be nothing you can do about it.
 
From the mixer's perspective, recording electronic drums is wonderful! No microphones, no acoustics, no phase problems, no bleed, no squeaky pedals, just easy editing and mixing.

I record drums using a Roland electronic kit into Sonar.
I use the USB out into the PC and can monitor the input with no latency.
I use Toontrack EZDrummer with expansion kits for sounds. Even my drummer thinks it sounds great!
 
 

There's always latency.. it might be so little as to not be noticed by most people. They say we can notice anything more than 5 ms. And if your recording the midi it doesn't really matter as it will get quantazied anyhow. 

I guess there must be some latency but it must be so low that I never noticed it.
When I play along to the other tracks while recording the drums they fit fine without being quantized.

Thanks very much for all of those responses.
The project is to produce a 4 song demo putting down the drum tracks first then layering the other instruments and vox in time honoured tradition. Playing live the drummer gets a great sound from his Roland kit which I'd be happy to record. How would latency be a problem if the other instruments are synching their playing to the original drum track?