Absolutely fine - connect as many as you like
However: currently the only computer that will be shown in the Engine Room on each device is the computer the client in installed on. Information about total mining between devices and other devices statuses has not yet been implemented.
While a combined speed is not indicated, it should be clear that the engine is working after a day of always-on mining. You will be able to see that your SpaceCoin balance is increased by the combined total of each PC's Coins per Day estimate
If you need help with connecting multiple PCs please let us know by filing a technical support request here: GFS Help Desk