I think you answered your own question. No artist operates in a vacuum. I'm sure Rihanna is perfectly aware of what's being said about her in the rest of pop culture.
Is it possible that Rihanna really is a "princess of the Illuminati" (even though the historical Illuminati was anti-royalty) and she and her producers decided to reveal that in a music video? I suppose so. But when it comes to extraordinary claims we as skeptics should require extraordinary evidence, and a playful reference to silly rumors made in a music video is hardly extraordinary evidence. It would be like claiming that Harrison Ford is planning to run for President of the United States because he appeared in Air Force One playing the President -- I don't think we need a denial from Harrison Ford to know that playing the President doesn't automatically mean you consider yourself a candidate.
Back on the subject of Rihanna, rumors about her being somehow involved with the Illuminati conspiracy that controls the world probably originated on the website The Vigilant Citizen. As far as I can tell the site's author is anonymous, though he claims some experience in the music industry.
I am also a music producer who has
composed music for some fairly
well-known “urban” artists. My work in
the music business has led me to deal
with talent agents, video directors
and record companies. Through my
experiences and my contacts, I have
discovered some of the darker aspects
of the entertainment industry, which I
found were in direct connection with
my studies in occultism. It is
necessary to understand of the state
of mind that prevails in the higher
levels of the music industry to “get”
the full meaning of the symbolism
found in music videos. Some things are
simply not intended to be understood
by all, they are meant for the “few”.
I can't say I'm completely convinced someone who's actually worked in hip hop field would put the word "urban" in quotes like that, but it's impossible to know what the writer's actual level of involvement is with the music industry so long as he remains anonymous.
The Vigilant Citizen (or as he call himself, VC) spends a lot of time deconstructing the lyrics and imagery in music videos and claiming to find the symbolism the Iluminati use to control the rest of us "sheep." Rihanna was an early target of VC, in particular the video for the song "Umbrella." Here's an example to give you an idea of what the website is like.
We then see Rihanna naked, covered in
chrome-colored liquid. Rihanna has
been raped by the Devil and covered
with his semen. She seems in pain and
not herself. On the frame above we see
her inside a triangle. This is VERY
symbolic. For occultists, an upwards
triangle represents the phallus, the
penis, male energy. Rihanna is inside
the triangle. She is completely
“owned” and under the spell of the
VC is also convinced that Lady Gaga is constantly revealing the Illuminati's plans in great detail to those who know how to read her videos, which is perhaps why Rihanna chose to be the princess of the group, not the queen.
While VC takes Illuminati conspiracy theories to a silly new place, that's not to say there isn't a kernel of truth in the claim that there's occult imagery in some hip hop music. There certainly is. The influential artist Jay-Z has been including occult imagery in his music for years. As Mitch Horowitz told NPR:
Mitch Horowitz, author of Occult
America, says that Jay-Z has a keen
grasp of certain esoterica, especially
in the music video for his new single,
"Run This Town."
In an interview with Guy Raz, Horowitz
pointed to Jay-Z's use of the phrase
"Peace God" as an allusion to the Five
Percenters. Also known as the Nation
of Gods and Earths, they teach that
the original black man is God — and
that all men are potentially God.
"Peace God" is a typical Five
"A phrase like 'Peace God' does not
find its way into someone's vernacular
by accident," Horowitz says. "He's
making a very definite statement."
Of course, Jay-Z would hardly be the first musician interested in the occult. Jimmy Page would be the classic example, and even in the world of hip hop Jay-Z was beaten to the punch by The JAMs (later known and The Timelords, and still later as The KLF). But the important point here is that just because some artists are interested in the occult that doesn't mean we should take that interest as evidence that there really is a worldwide conspiracy to mind control to world's population through symbolism. Real evidence for the Illuminati claim has never been presented.