Yes!
If a computer system has both PCI/PCI-X and PCIe slots, the UAD-1 and UAD-1e can both be installed and used simultaneously as a multicard system.

But:


PCIe should not be confused with PCI or PCI-X. PCIe is not compatible with PCI or PCI-X because it uses a completely different connector. The UAD-1 will ONLY work in PCI and PCI-X slots, and the UAD-1e will ONLY work in PCIe slots.