Size and Strength: Rabbits are significantly larger and stronger than hamsters. This makes them a potential threat to the hamster, even if they don't intend to harm it. A playful bunny hop could easily injure a small hamster.
Territoriality and Aggression: Both rabbits and hamsters can be territorial, especially when it comes to food and their living space. A hamster might feel threatened by a rabbit's presence, leading to aggression and fights.
Different Needs: Rabbits and hamsters have different dietary needs, housing requirements, and exercise patterns. A rabbit needs a large enclosure with plenty of space to hop and run, while a hamster needs a smaller, more secure cage. Their dietary needs also differ significantly.
Risk of Disease Transmission: Though less common, there's always a risk of disease transmission between different species, even if they are housed separately. This is especially true for rabbits and hamsters, who can carry different pathogens.
Conclusion: While it's tempting to think of a rabbit and hamster as friends, it's not a safe or healthy combination. It's best to keep them in separate enclosures and provide them with the appropriate environment and care for their specific needs.