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Of Course it does matter, In almost all cavy care websites it is always written that Guinea Pig Pellets are formulated specially for them, mainly of the Vitamin C issues.
Here's a good reference from
Guinea Lynx
Plain dye free high quality guinea pig pellets (mixes with nuts are considered too rich), formulated with Vitamin C can be provided in a small heavy ceramic bowl to prevent tipping and cleaned daily. Each cavy will eat approximately 1/4 cup of pellets a day. Purchase pellets in small quantities and store in a dry cool dark place to preserve the potency of the C (look for a pellet with an expiration date to check for freshness). Kaytee offers a plain pelleted product (Forti-Diet) that uses stabilized vitamin C and has a "Best If Used By" date to ensure quality.
Most cavy pellets are alfalfa based. Alfalfa pellets are suitable for young, growing and pregnant cavies. A timothy based pellet (less calcium) may be a good choice after they are about a year old and fully developed (notes). Oxbow Hay Company makes a timothy based pellet called Cavy Cuisine.
And here's another from the (broken link removed)
When choosing your pellets, be sure to avoid the guinea pig "mixes" that contain nuts, seeds and dried fruits. These mixes are high in fats and oils, which can lead to excessive weight gain. Additionally, many of these mixes contain sunflower seeds in their shells. Guinea pigs should never be fed nuts or seeds that are still in their shells (peanuts, sunflower seeds, etc.): dozens of guinea pigs in the Pacific Northwest alone die each year from choking on these shell fragments.
