A spectrum analyzer, in its purest form, measures signal strength versus frequency and does not inherently know anything about modulation.
There are spectrum analyzers geared specifically toward satellite use, as I suspect you've seen. These will typically trade bandwidth options and perhaps accuracy in exchange for adding features like demodulators and MPEG decoders.
So to your question about whether it matters if it supports a particular modulation standard, well, this comes down solely to your personal preference and goals. Any spectrum analyzer (with an appropriate frequency range) will give you signal strength information that allows you to perform precision dish peaking and quickly find new carriers that pop up. If, say, you'd find locking a DVB stream and viewing video to help identify a particular satellite helpful, then consider that kind of analyzer.