Which also presents an 'interesting' question. Who is being defined as a "rebel"?
A citizen of Ukraine resisting or fighting against the government of Ukraine would (normally) be a fairly clear cut example. However, given that Russia granted or offered citizenship to Ukrainians prior to annexing the Crimean, much like the did with some Georgian citizens immediately prior to occupying South Ossentia in 2008, this introduces the whole potential for a person to switch from being a Ukrainian to a Russian citizen, fighting in the Ukraine. And of course the foreign fighters combatting Ukrainian government forces are not rebels, but more likely unlawful combatants participating in an internal conflict.
On a related note, what is the real status of the "Ukrainian" refugees who have crossed the border into Russia? Are they Ukrainian citizens? Are they amongst those taking advantage of the offer of Russian citizenship? Are they looking to return to their homes in the Ukraine? Are they looking to return to their homes, but have those areas be part of Russia?
Between the propaganda, spin, disinformation, and misinformation coming from basically all sides, it makes the situation quite hard to get straight.
Also, please note when I reference Ukrainian vs. Russian citizenship, I am not meaning their ethnicity, but what they have citizenship from, and/or can get issued a passport by.
The offer of Russian citizenship to Ukrainian refugees now residing in Russia is a fairly recent thing, if I recall correctly, so they can settle down and work instead of sitting around being refugees for months on end. One would imagine that only those who don't plan to go back to Ukraine (for whatever reason -- home destroyed, distrust of the government, bleak economic future, etc.) would opt to become Russian citizens. Many Ukrainians, especially those in the east, had been working in Russia for years and years anyway, while retaining Ukrainian citizenship (sort of like Croats working in Germany).
What the plans are of those who have not opted to acquire Russian citizenship we can only guess, but. the most straightforward answer is they probably hope to return home when it's safe and the fighting is over and services have been restored. Putin declined to annex eastern Ukraine when they asked for it, and they probably have no illusions there.
Of course the Ukrainians who have crossed into Russia are Ukrainian citizens, unless they have elected to take up the offer of Russian citizenship. (Can they be dual citizens? I don't know.) I'm not sure why a Ukrainian fighter in Ukraine would leave the fighting, skedaddle over the border as a "refugee" to claim Russian citizenship, and then return to the front in Ukraine. It doesn't make sense, but I suppose it's possible a few individuals may have done so.
Yes, all the disinformation from all sides does make for a confusing mix! That's why I'm especially grateful for this sane place and Feanor's excellent updates and analysis.
As said, the definition of rebel is problematic. Consider Strelkov, for example. A Russian from Russia. Not a Ukrainian of Russian ethnicity, nor a Russian of Ukrainian ethnicity, but a Russian of Russian ethnicity.
From all reports, there are many such. The small fragment of the Russian press which doesn't publish what Putin tells them to has claimed that Russians have been recruited in Russia (specifically, in the report I read, in Rostov on Don & surrounding areas) through Russian army recruiting offices, to fight in Ukraine. It reports that recruitment has been active, with potential recruits being contacted directly - e.g. unemployed veterans of Chechnya, Afghanistan & other wars. It looks as if prior experience is considered more important than youth, & the recruiters have access to records of other agencies, which points to a co-ordinated government operation. The reports say that they've been paid & equipped by Russia, & the bodies of some such recruits have been returned to Russia for burial after being killed in Ukraine..
It's hard to see how such people can be called rebels, any more than Strelkov.
My Russian is pretty rusty these days, but what I've read is that "the rebels" have set up recruiting stations inside Russia, not that they are being recruited *directly* through the Russian Army. I've no doubt that perhaps the Russian military establishment may be assisting the effort by way of providing contacts, checking records of applicants, etc., behind the scenes, but I simply haven't seen the reports you mention. That's interesting. Could you provide a link or source?