Guinea pigs can eat iceplant in moderation, as it is safe for them. Iceplant contains some beneficial nutrients and moisture, which can be a nice addition to their diet. However, it should not replace their main source of hay and should be offered alongside other safe vegetables and fruits. Always introduce new foods gradually and watch for any adverse reactions.
Mesembryanthemum crystallinum is commonly called the Ice Plant but Sedum spectabile is also sometimes called it too. This shows the best argument for using the Latin or scientific name where possible.