I haven't been here long, but I get that tipping is a bit of an issue...
As an Australian, we do not have a tipping culture at all.
Having read a bit here, would it be appropriate to tip $5 if I see the SCA, and $0 if I don't see them at all?
The discussion of tipping is like a reoccurring nightmare!
I tip the SCA $5 because I don't need anything extra, just for my bed to be made. As mentioned if they go an exceptional job, you may want to increase it to $10. But it would also depend on how many nights you're traveling too.
Now just as a sidenote, I am a cafe attendant, and during the touristy times of year I will get travelers from all over the world (just on Saturday I had multiple British and Chinese families/groups, and a family from Australia as well), and I try to be very recognizing about other cultures and tipping habits. I have said this many times and I'll say it again. I take no offense if I don't receive a tip, no matter the culture, provided you simply are friendly and thank me. I can't say we all are like this, but plenty of us are!