It depends on at least a couple of things, IMO.
1. Are you using software which (at least attempts to) adjust times run on poly to today's dirt surface (i.e. by an inter-track variant). If so, experiment to see if you can trust that adjustment. For example, in RDSS, after we get done adjusting and projecting and equalizing surfaces and distances, you're not handicapping a race at (for example) Hollywood Park (or Woodbine) anymore - you're working it at some hypothetical 'normalized' location (sometimes affectionately called 'Sartin Downs'). It's a separate issue whether one 'believes' in adjustments, or likes TrackMaster's.
2. Has the horse proven (or not disproven) that it has an affinity for poly (or for dirt, if it has so far run only on poly). If not, 'caveat emptor' - same as for Turf. Wait until you see if the horse tells you something first.
Some believe (i.e. from their analysis and betting experience) that, for example, a poly line works as well as a Turf line for rating a horse at Woodbine on either surface. Shipping in there, from dirt surfaces, less so. In my personal experience at Woodbine, I let RDSS' ITV adjustments do their work, then let Matchup and other analysis find the contenders. I'm usually not seeking to bet 1 horse in the race anyway, so a little uncertainty is tolerable.
FWIW
Ted