I'm considering buying the Royalty DLC for my new playtrough, however, as my plans for the group I'd play as involve refusing to do anything for the Empire, and only fighting them when the opportunity arises (I've read there are some quests opening the possibility?), is that possible without doing anything -for- the Empire in the first place?

"For some definition of."

Every single playthrough with the DLC I got these two quests in short succession:
- protect an Empire citizen from wildlife (gain first imperial title, open up other pro-Empire quests)
- protect an Empire traitor from loyalist pursuers (gain Empire site on the world map, which you can raid for Psylinks; become enemy of the Empire)

The second quest definitely is "not doing anything for the Empire", but it is an Empire quest for Empire citizens, so depending on how strict your requirements are, it might or might not suffice.

There ought to be a few avenues I have not yet tested but which *should* work and might suit your palate better:

- accept first quest, capture Pawn instead of protecting them (slightly better than doing the second quest: one never helps anyone affiliated with the Empire in any way - one merely lures them in and immediately crosses them)
- wait for Imperial Tribute Collector caravan and attack it (unsure whether it appears without any Empire title)
- attack Empire settlement, mayhap shoot a few things or people with Sniper Rifles or Mortars (or just sacrifice some suicide pawns)

As soon as reputation with the Empire is ever so slightly negative, the Story Teller should use them in the pool of hostile factions for normal events.

So far I have *not* seen travellers "passing through" or regular traders from the Empire, who might be attacked for a straightforward reputation loss. From the wiki, those do not seem to exist.