Absolutely good malt for a lager. There are plenty of them in Scotland (its really just their version or Maris Otter). Go for it. It should result in a maltiness backbone similar to a Pilsner Urquel (Czech) or Bitburger (German)
Don't be shy about brewing outside the style guidelines on this. You can make some great hop forward lagers using ingredients you'd normally use in an ale. I did one using MO recently and loved the change from pilsner malt.
GP seems to bring forward more sweetness in the finished ales I have made compared to MO, I would imagine that sweet malty backbone would carry into a lager as well. Now I want to try a GP lager SMASH! I use a LOT of GP!
20-30IBU range would be my choice. Just enough to notice the hops but not enough bitterness to over shadow the malt. GP will have fewer enzymes than most base malts giving you some color and flavor more diastatic grains would convert to sugar quickly.