As to the metal models, some of them do and some don't. I own all metal Frostgrave soldiers and a couple of wizards. Few of them are true giants when compared to the rest. I was dissapointed by the size and proportions of the marskman and particularly the Nickstarter knight (although they make pretty nice figures on their own). Most of the Frostgrave range are more realistic sculpts quite close to the standard LOTR minies.
As Joe has pointed out, even LOTR miniatures do vary in scale, so it depends. But in general, Frostgrave and LOTR fit together much better than to Warhammer