Like I said before, the question lies in the game's definition of placement. Also the rules never refer to a scatter marker. It specifically refers to a model. Also you keep talking about the Scatter Marker, a concept I believe went away in 4th (maybe third) edition.
Additionally on page 13 it explicitly states "Remember that other models, friends and enemies, also count as impassable terrain". Combine this with a line from page 14 "Models may not be placed in impassable terrain unless the models concerned have a special rule in their profile granting them an exception (like being able to fly above the terrain) or both players agree to it"
So in conclusion :
1 ) Deep strikes start with models being placed
2a ) Other models are impassable terrain
2b ) You cannot place models in impassable terrain
ergo
You cannot place the mawloc on top of other models.
Except of course those implicit in all cases of placing a model on the tableYou can 'if' all you want, but this is a rule forum, and we try to stick with whats written in the rule books. The Deep Strike rules provide no restriction for the deep strike marker (the model) when placing it on the table.
There's no implication of this line of reasoning anywhere in the deep strike rules. Just an fyi.The problem here is that you are some how treating the marker (the model) as 1) an actual model that is bound by rules given in the rest of the book (which is isn't) and 2) actually on the table (which the unit has not reached the table yet).
You can place the model anywhere that the Deep Strike rules allows, which is anywhere on the playing field (the table). Where you place it initially is NOT important as the unit is not on the table yet. Thats what the Scatter Roll determines.
EDIT (since 20 minutes isn't enough time for the 30 second timer to be appealed) :
Now to fix this problem. Personally I'll be going with the following errata on the rule (not saying I have any authority to issue such, just what I would do to fix it)
Replace the first paragraph of the Mawloc's "Terror from the Deep" rule with the following :
If the Mawloc arrives via deep strike do the following. First nominate a target point. Then roll a scatter die and 2d6 scattering that point accordingly. If the point goes off the board the Mawloc suffers a Deep Strike Mishap on the Deep Strike Mishap table. If the point is still on the board center a 5" S6 AP2 template on the point
<insert rest of paragraph 2 about models being moved and the like here>. After this has been resolved the Mawloc deep strikes without scattering on that location. Resolve any mishaps from impassable terrain as normal.