There seem to be a lot of different versions of sambal oelek. My favorite is an Indonesian chili paste which I could buy at the grocery store in Canada. It's not, unfortunately, available where I live, so I'm forcing myself to make it from scratch, which is a bit difficult in that the peppers are completely different here, so it ends up being not the same as I grew to love. My favorite incantation was red chillies, vinegar, and salt. That's it.
Sambal oelek can be as simple as ground chillies and salt. Or it can have vinegar in it as well. It can have garlic or ginger or onions or carrots or sugar added, as well, and I wouldn't doubt that there are other variations available on top of those. From what I've been reading, it depends on the region where the sambal oelek is from.