Time Machine: many different Macs on one disk?
Yes, sharing a single drive amongst several Macs is doable. For more details, here are some resources to review:


This Apple.SE question may provides some pointers, such as not using File Vault 2 when sharing the drive with Macs running OS X prior to Lion. 
Another Apple.SE question provides some suggestions for network backup. 
Other discussions (such as this post) recommend using multiple partitions on the shared drive.