I don't think they'd be a good choice unless your piggies are fully litter trained. They'd be hard to fully wash and get the urine out.
What you can do though is what Robin said. Simply sew a towel under a fleece blanket like so. (blue is fleece, black is towel)
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Or, you can litter-train them which is very easy! Then you can use those bath mats.
Another option is using those bath mats and cover it with fleece.
Another option is fleece ontop of pee pads.