NO! It's not right, sadly it's still quite common advice
Neither the RWA or RSPCA advocate the keeping of these species together.
Rabbits can injure guinea pigs either because they try and hump them (especially as chances are a rabbit kept with a piggie won't be neutered), deliberately 'bully' them, or even if they seem to love each other, if a rabbit is startled, its big feet can easily break a piggie's back. Rescues will be able to tell you all sorts of horror stories about the injuries they have seen on piggies kept with rabbits, and how much happier the piggies seem to be once they are separated.
Also their diets are different - piggies need constant access to their food whereas buns should only be given a handful daily and the rest of the diet as hay. The protein/fibre ratio as well as various vitamin amounts in the foods are different, so in the long term it's not best for either of their diets. Piggies also need additional vit C which isn't necessarily a problem as this can be given through veg, but still something to consider.
Finally bunnies can naturally carry a type of bacteria (Bordatella something) which can cause a serious illness in piggies.
Oh and of course they don't understand each other's 'language' they are entirely different species with different ways of communicating, so are best kept with their own kind!
When you see your (neutered!) bunnies together like this, it defies all logic to say that they shouldn't be kept together!
There's nothing wrong in using straw for bedding, mine seem to prefer it as it's a bit softer and seems to insulate better. If they eat it, it has no nutritional value but it's not a problem. I guess being told not to use straw is ok if you are being told to use hay instead - as constant access to hay is important, maybe people use straw instead of hay, so they advise not to use it as this automatically makes more people use hay :?