O/T Guitarists - Advice needed on Guitar Tremolo

Hey Classicman-
    First, yes it can be confusing as electric guitarists often refer to the whammy bar as a tremelo bar.   Single note tremelo parts can be very common and written out pretty fast for rock guitarist.
Jump to 2:45 for an example http://www.youtube.com/watch?v=z_lwocmL9dQ   
 
For flamenco type of music you have http://www.youtube.com/watch?v=8Gzhc7b-ruI which you will need a guitarist that can fingerpick well...your not going to find alot of 'rock' players that can pick like this.

For your example,  a guitarist can certainly tremelo a whole chord. If you want a guitarist to tremelo the entire D9 chord, I would simply spell out the chord on the staff in whole notes and put the appropriate slash (tremelo) marks either 8th or 16th notes.  I would be hesitant to write out anything faster than 16th notes unless you have a really slow tempo or you know your guitar player can handle it.

A few more thoughts - the classic electric guitar vibrato done with the fingers only takes the note sharp of it's original pitch - not alternating flat-pitch-sharp like a violinist's vibrato. The vibrato is made by rapidly bending the string a little sharp then back again.

Finger vibrato can be applied to more than one string at a time, but tends to be less fluent and as the strings don't get bent the same amount each tends to be a little detuned as well. Some guitarists will loosen their thumb on the back of the neck and shake the guitar with their left hand to vibrato chords.

It's also possible to vibrato say one note out of a two or three note chord.

The tremolo bridge (as Leo Fender called it) or vibrato bridge (as Bigsby and Gibson correctly call it) can take the pitch flat as well as sharp.

Synthesising realistic guitars is very difficult - one thing to watch is that a guitar can't play all possible combinations of notes as it would require an impossible stretch, and other combinations that can be played are difficult to get to "in a hurry" so tend not to be used much. And chords are rarely in quite the inversions a keyboard player would naturally go for.