Is there a funk scale, akin to the blues scale?
If you use the blues scale, you won't be going too far wrong.
The defining feature of funk is its rhythms. If you're looking for a specific tonal feature of funk, try this guitar tab, a simplified version of the riff which forms the vast majority of the song Another Brick in the Wall Part 2 (We Don't Need No Education) by Pink Floyd (The dash represents a hammer-on):
e 5 5 5
B 6 5-6 6
G 7 5-7 7
D 7 5-7 7
A 5 5 5
Basically, what we have here is a Dm chord (which in this case goes on for ages) punctuated by an approximation to a Cmaj chord formed by the notes of the barre. C is of course the (minor) seventh of Dminor.
This use of barred minor chords punctuated by the "chord" that happens to be formed by the open bar, strums of muted strings, and several other modifications of the basic minor chord are an essential feature of funk.
The bass will be playing the roots of the chords (generally minor) with frequent use of the sevenths of those chords as passing notes, plus complicated scale runs and (if you want to bluff it) the "disco" rhythms formed by playing two different root notes an octave apart.
Take those rhythmic elements away and listen to a saxophone, keyboard or guitar solo on its own, and you will be hard pressed to identify the music as funk (as distinct from blues, jazz or rock.)
So you will be using normal diatonic and pentatonic scales, particularly the minor-sounding ones (dorian, the aeolian/minor scale itself, phrygian) and of course the blues scale.