If it's a really slow internet connnection, since Lion is a 4GB file, itls more than likely the download will time out before the download is completed.
And just so you are aware, if Lion is installled, if the startup disk needs repairing or the Mac OS X reinstalled, it requires high speed internetc (broadband) connection to do so.
Requirements for reinstalling OS X Lion
"Reinstalling OS X Lion via Lion Recovery requires broadband access to the Internet via Wi-Fi or an Ethernet connection. OS X Lion is downloaded over the Internet from Apple when Lion Recovery is used for reinstallation."
From here > OS X Lion: About Lion Recovery
An alternative would be to purchase the OS X Lion USB Thumb Drive - Apple Store (U.S.)
Yes, it can.
If at some point they have a faster internet connection, if they alraedy purchaseed Lion from the App Store, they can re download Lion for free using the same Apple iD and create another install disc if they want to.