Shame there are no photographs of the sessions - none of Bowie actually playing instruments, that is. The guitar is definitely not equipped with single-coils - even through the heavy treatments (chorus, etc), the guitar sounds has too much grain to be anything Strat-like. My guess would be a Les Paul or an SG, at least, something with humbuckers an easy access to the top of the neck, with every part doubled or tripled-up to get that nice, George Harrison-type sound on Sweet Thing & We Are the Dead. But it's really hard to tell.
I found this http://www.freewebs.com/theyearofthediamonddog/diamonddogssessions.htm
but I question the accuracy of some of the details; the author seems confused about Visconti making use of the Eventide Harmonizer on the album:
"The Eventide digital delay processing unit is one of the first of its kind, capable of changing the pitch of a signal without sacrificing the tempo. This means that a vocal or guitar can be fed into the Eventide enabling the pitch to be raised or lowered. This effect can be especially heard on David's lead vocal track during the 'Sweet Thing' suite."
(Only Bowie's tenor range - no electronics!)
Which reminds me - his saxophone playing throughout the album, although not too demonstrative, is really neat and interesting. It is not that easy to hit the low notes on a baritone sax with an untrained embouchure and stay in tune, which makes me think he hadn't been too out of practice on the instrument at this point.
Sorry, I hope I don't bore you guys with my musician spiel.