Used an RTL-SDR and SDR# to analyze my IC-7300 SSB signal into a dummy load. Seeing IMD products at -32dB relative to the main signal around ±6kHz from center frequency.

At more than 6 kHz separation the distortion energy level should be at least -40 dB compared to the pass band signal. A reasonable criteria for poor quality SSB signal is one that has a width greater than 6kHz at 40dB down.

My settings: MIC 50%, COMP 3, using SM-30 desk mic. The -10dB bandwidth looks good at 2.8kHz, but those IMD products worry me. Is this acceptable for general operation or should I back off the compression?

Running 100W into MFJ-264 dummy load, no amplifier in line.

If a station exhibited this type of signal over the course of a contest or generated complaints from participants, it could be subject to disqualification. You're borderline but not terrible. Try reducing COMP to level 1 or 2 and remeasure. The SM-30 is a good mic for that rig.

They crank up the microphone gain and speech processing, and end up over driving various stages resulting in distorted transmit audio due mainly to excessive IMD. The manual states to adjust until the ALC meter reading swings between 30 to 50% of the ALC scale. Check your ALC - that's usually the culprit.

Your IMD at -32dB isn't great but not horrible for casual operation. Too much proc level will make it sound harsh and drive background noise. You want minimal processing to help boost sharpness, then proper drive for good ALC indication. Less is often more with modern rigs.