According to a bunch of French researchers who study prosody: No.
I learned this at a prominence workshop at Speech Prosody 2010. I asked Mathieu Avanzi why, in his paper "A Corpus-based Learning Method for Prominence Detection in Spontaneous Speech", he and his co-authors looked at pitch, duration and pause features, but not intensity or spectral emphasis. The response: "Intensity does not correlate with prominence in French".
Now, I don't speak French, so far be it from me to comment on what is perceived as intonational prominence in French by French speakers.
Intensity correlates with prominence in (at least) English, Dutch and Italian. So my curiosity was piqued.
At the same workshop, Mathieu and others released C-PROM, a corpus of French speech which has been annotated for prominence, and labeled by French speakers no less!
So I figured it would only take a few minutes to check it out. Using the feature extraction routines in AuToBI, I pulled out mean values of pitch, intensity and duration for each annotated syllable. Armed with a t-test and R, I looked to see which if any of these features correlate with the labels of prominence. (For this analysis, I collapsed the annotations for strong and weak prominence.)
So, let's look at the data.
The bimodal distribution of mean pitch is almost certainly due to the presence of male and female speakers in the C-PROM material. But even without any speaker or gender normalization of pitch, we can still evidence of the correlation between mean pitch and prominence. The mean value of prominent syllables is 185.6Hz compared to 158.0Hz for non-prominent syllables. This has an associated t-score of 24.117 (p < 2.2*10^-16).
This result is even clearer. Prominent syllables are on average 97ms longer (261ms) than non-prominent syllables (164ms). This has a t-value of 54.240 (p < 2.2*10^-16).
Well there it is. It's not as pronounced a difference as the difference in pitch or duration, but the data shows a clear correlation between mean intensity in a syllable and whether the syllable is prominent or not. Prominent syllables are on average 1.6dB louder than non-prominent syllables (72.08dB vs. 70.48dB). This corresponds to a t-value (15.174) that is lower than that seen in the pitch and duration analyses, but still significant (p < 2.2*10^-16).
Now...This is clearly a very basic analysis of correlates of prominence in French speech. But based on these results, I'm comfortable answering the question now.
Does intensity correlate with prominence in French? Yes.
[edited at 12:43pm 6/16/2010]
Following up on a comment from Raul Fernandez, I thought I'd post a parallel plot on the correlation of intensity and prominence in English.
Rosenberg & Hirschberg 2009).
Here we find a similar difference in mean intensity (1.9dB) between prominent (60.8dB) and non-prominent words (58.9dB). This has an associated t-value of 21.234 (p < 2.2*10^-16).
There is little controversy about the correlation of intensity with prominence in English. (In the last few years, there has been work even suggesting that intensity is a better predictor of prominence than pitch, (cf. Kochanski et al. 2005, Silipo & Greenberg 2000, and Rosenberg & Hirschberg 2009).) Of course, this chart doesn't indicate that there are equivalent relationships between intensity and prominence in French and English -- merely that the French correlation deserves more attention.