I don't know of any tool that can extract samples from MultiPCM VGMs. Ripping from the VGM files directly also might be a bad idea as they are usually stripped from samples that the song doesn't use.
However, it should be pretty simple to write a small program that rips the samples from the MPR files.
At first you need to combine the sound ROM files so that you get one file per
region defined in MAME. (e.g.
mpr-16491.32 and mpr-16492.33 result in one one, mpr-16493.4 and mpr-16494.5 result in another one)
Each of those files begins with a sample table that contains up to 512 samples, with 12 bytes per sample. You can look at
this code in order to get an idea of the format. (Or look it up in the YMF278B/OPL4 manual - it's the same format.)
A small note: SEGA's arcade boards use some special logic to access anything past the 1 MB mark. Feel free to ask us about that on IRC.