Yes he is.
He did guest lead guitar on this Porcupine Tree song too:
Quote from Wiki "The track "Nil Recurring" is an instrumental piece and features King Crimson guitarist Robert Fripp on lead guitar. As well, drummer Gavin Harrison plays tap guitar on this track."
Source: https://en.wikipedia.org/wiki/Nil_Recurring
Song: https://www.youtube.com/watch?v=_xt6E5d4opI
He did guest lead guitar on this Porcupine Tree song too:
Quote from Wiki "The track "Nil Recurring" is an instrumental piece and features King Crimson guitarist Robert Fripp on lead guitar. As well, drummer Gavin Harrison plays tap guitar on this track."
Source: https://en.wikipedia.org/wiki/Nil_Recurring
Song: https://www.youtube.com/watch?v=_xt6E5d4opI