On their own, each is a compelling DAW to begin music for picture, or deliberative development: offering a radically different mindset towards music and score creation individually, could the combination offer a real game changing workflow?
With Live the creative hub and Pro Tools the video host, tempo conductor, sync timeline, [and eventual content delivery format, for printing stems prior to distribution, this offers a great workflow for sketching out film scores over long periods of content.
Cons with this Multi-DAW configuration: In ReWire Slave, Ableton Live offers no VST/AU plugin support. Thus, this specifies Ableton's role to being more of audio loop host/MIDI sampler, triggering any sound in the film flexibly via MIDI command.