Altera provides Device Pin Connection Guidelines which have power supply sharing recommendations both for supplies used by the FPGA, and supplies that can be shared across multiple FPGAs. As a general guideline, any supply which can be shared with other supplies within one FPGA can be shared with multiple FPGAs provided they require the same voltage level.
For Power Distribution Network (PDN) design though, you need to take into account system considerations to maintain a stable power supply and meet the ripple requirements for all of the devices sharing a common power supply on the board. Activities from one device may interfere with another or other devices due to noise coupling on the shared power rail.
A complete PDN analysis on transfer impedance helps to evaluate the risk with interference from multiple devices through noise coupling. However, this requires a wide set of component and PCB specific information and some model extraction software which may not be readily available for analysis.
Altera provides the PDN Design Tool to assist in obtaining the required decoupling for a single FPGA on your board, but it does not capture the potential interference from other devices sharing a common power supply. You should use good PCB layout practices to help reduce the noise interference risk. Refer to the Board Design Resource Center for further information.