Will it be possible to use a tool or something that an enemy has made? For example, you use wooden spears, and the enemy has found a way to make stone spears, will you be able to use them after killing one of them? I'm not talking about immediatly being able to build it, but just use it (For example, a lot of native Americans used guns that they stole from carriages)? Also, will you be able to capture buildings? because in most rts's, you have to destroy all building that the enemy made, even though you should be able to just use the houses/other buildings..
Then we can reverse-engineer it, especially applicable to simple tech like stone spears over wood.
That would be pretty hard, as for a lot of things, making it was the hard part, not "getting the idea"/designing it... (For example, there had to be made a lot of improvements to flint-knapping to be able to make sturdy enough, but also sharp enough points for spears... (I also never got my answer to the question...)
I think you're answering your own question, actually
We don't have some plan set in stone yet, so we're free to just come up with something through discussion. With that in mind, I'd guess that we should be able to acquire artifacts from other cultures without learning how to make them, and 'reverse-engineering' might be able to let you learn how to make them.
And I agree that it should be possible to capture and use or repurpose items, buildings, etc, which you acquire from someone else. You might be bad at using them, or bad at repairing them, but this would greatly depend on what exactly it is that you got. There's a reasonable case that even the original owners/builders of an object might not be that effective in their use (eg, tanks and tank doctrine).