I've just played and Empire army, reading the 8th ed. line of sight rules, as drawing line of sight from the eyes of the figure shooting, to a vital bodypart of the target. Though this is how it's written in the BrB, the example they give on targeting one unit behind another is where they target Cavalry behind Infantry. By these rules you essentialy can't use skirmishers to block line of sight, preventing saurus from being shot at? - Or CAN you infact do this aslong as they are of the same unit type? (Eg. Inf blocking Inf, Cav blocking Cav etc.)
I think if you can target through skirmshers (which seems possible at the table level), you should first talk to your opponent to make sure you agree. Then, the unit that you are shooting at should get a cover save (of -1 soft or -2 hard).
See my explanation of the line of sight rules on this thread.. http://www.lustria-online.com/threads/shooting-through-and-over-skirmishers-in-8th.4544/ Has nothing to do with troop type, but it is in fact true line of sight. Skirmishers will essentially always allow enemey units to shoot through them, but there will always be a -2 penalty, as UNITS count as hard cover. Only things like trees and fences give the -1 cover. So yeah, they can shoot at things behind skirmishers, but at a -2, which is a win in my book.