I've read several other questions about material in order to learn RoR. But my question is can I start learning RoR without Ruby?
It's clear that the other way around is better, but I would rather try this way if it makes sense (somehow). Or learn both in parallel...
                 
                                                                            
                            Well, given that Ruby on Rails is just Ruby written in a particular fashion (read: framework) yes you will need to learn Ruby.
You will need to learn these things about Ruby (amongst other things):
- Everything Is An Object. Everything. Yes, even 
2 and "foo"
 
- Class Inheritance and What It Does(tm)
 
- How to tell the difference between class and instance methods
 
- Modules and how to use them correctly (
class_eval Is Your Friend) 
- People write gems. Use them. Re-inventing the wheel is fine and dandy for learning but re-inventing it because you think your method is better is not.
 
And these things about Rails:
- Do not fight conventions.
 
- Do not fight conventions.
 
- Model code goes in the model. 
 
- Controller code goes in the controller.
 
- View code goes in the view.
 
- Helper code goes in the helper. 
 
- Ask yourself "Does Rails have a helper for it?". If the answer is "No" ask somebody else. The answer is likely to be "Yes".
 
And these things in general about learning:
- Google it.
 
- Google it again.
 
- If the answer you seek is not within Googling distance, formulate it in a way that is kind to those who may know the answer (such as you've done with this question!) 
 
- Appeal to people's greater motives. How can helping you, help them?
 
- Try not to be too much of a help vampire.
 
- If asking in an IRC channel, use a pastebin service such as http://pastebin.com, http://pastie.org or http://gist.github.com
 
- Second rule about asking in IRC: Don't ask "any ideas?" after your question. Your question should already ask this by itself.
 
And finally: Love what you do.