Well, birds can technicaly be considered dinosaurs, but that's beside the point...
The main problem with any Loch Ness creature is that in order to survive there would have to be a large enough number of creature to enable genetic fitness. I forget how you work it out exactly, but in order for a species to survive and not become "inbred" the community has to be fairly large, and I don't think that Loch Ness is big enough to support this.