I didn't see an answer in any other threads and I don't remember seeing anything in the printed material, so I'll ask it.
Can player side quests be used in the Helm's Deep scenario?
If so, how are they handled? It would be pretty cheap if enemies would quest them out for you and it would be a mighty stretch of the written rules if players could put progress on them in that scenario.
Side quests are allowed, and they are handled as per usual. Note that the rules for the Defense keyword specifically refer to it applying only if the current quest has Defense (true of Battle, Siege, et al., of course, but particularly important here), so no, the encounter cards aren't going to do your side quests for you.
See Caleb talk about it himself here: https://boardgamegeek.com/article/19675718#19675718 (where he also generates the Devilry of Saruman erratum).
Edited by sappidusThat makes sense. Thanks!