1. Can I import a hardware wallet into a mobile wallet like metamask?
If you can export your metamask wallet to your hardware wallet, then be rest assured it is possible to export your hardware wallet to metamask, all you need is a private key or seed phrase.
2. What are the risks involved in doing this?
Risk involved is that metamask is more like a hot wallet and stands a higher risk of getting hacked, there are many phishing sites, even viruses and malwares targeting metamask users, if your system gets infected with a virus or malware, you stand a chance of loosing funds stored on your metamask wallet easily.
3. I want to bridge Arbitrum will it work on hardware wallet?
This I can not answer because I've never used a hardware wallet, all I know about hardware wallet are based on my research.
So I think other users that have used hardware wallets will be in the best position to answer this question.