And it is possible that what was found wasn't in that hex, but could be seen from that hex such as a Gun HIP is OG.
I don't think that dummies are eliminated just because they might have LOS to something, only if they try to enter a location with concealed/hip units/items. Entry into hexes with mines is covered in A12.11, while entry into hexes with other units is covered in A12.15. Entry into hexes with other fortifications is covered in E1.16, and that is also used by G.2
As far as situations where a moving concealed stack has LOS to something but is not entering that location, I don't believe there is an "official" rule. There is a q&a:
A12.2 & A12.33 What do you do when a concealed stack that may be a dummy stack moves into LOS of your HIP 5/8" counter/-Fortification?
A. One way to handle this is for the defender, before the stack gets into LOS of anything, to ask if the stack is Good Order yet. Another is for the defender to wait until the stack is in LOS of something before asking this question. [Compil3]
This does not say whether the player with the concealed, moving unit is obligated to state truthfully whether the stack is Good Order (dummies are not Good Order). It could be that it is optional, i.e. the moving player might be able to decline to declare that the stack is good order even though it is. Whether or not the moving player is obligated, there is nothing that says the dummy is removed just for not being good order and so unable to put the sighted item on board. There would have to be some other reason to remove the dummy, e.g. movement in the open or non-assault movement while in LOS of an enemy unit.
Personally I play by saying, "you might be able to see something there. Do you want to claim that is a good order unit?" I let my opponent choose whether to declare the unit good order or not.
JR