I am pretty sure the ritual attacks always happen before normal ones, and I have used that trick for times. But in my recent MP I did once see my scouts attacking the local PD before horrors did. (Attached is the report from two provinces, and both scouts attacked their targets in the ritual phase, simply before the site searching)
I believe something unintended is behind it, and would like to track it before the reporting in the bug tread, has someone else idea for that? I can also afford the save and result file if that helps.
That's if the scout is located in the same province as the horror, therefor he'll join the battle.
When using horrors you must send a scout from an adjacent province.
Same with ghost rider, or any other ritual like that.
I have never done so before however I read in some guide that if you send horrors at the provinces A and B and attack A from B with the scout you own both.
Looked like a bug though, so it's more like fixed.
Horrors are counted as special monsters and have independent nation id, thus the battles will always be separated.
And I do think if your sneaking amry attacks the province which they have been already in, the battle will also be resolved in normal battle phase, hence after Horrors/Ghost Riders.
Edit: Hmmm... Zeldors word seems to be the key. Another good lesson for me. Thanks all.