Yes, the Staking Pool is shared by all Virtual AMMs.
Each lock-up time, or "epoch", as we call it, lasts for 7 days. The length of the epoch can be adjusted through governance.
Rewards given to stakers are available right away for fee rewards, and locked for 1 year for trading fee / funding payment reimbursements (80% locked for 1 year, 20% available immediately).
The primary risk is exposure to volatility due to the 7 day epoch -- if the price of PERP changes in relation to other assets, you will be unable to swap it before the end of the epoch.
In general, staking on Perpetual Protocol does not expose you to IL (impermanent loss) because you are staking a single asset. Your can always withdraw the same number of PERP as you initially staked.