There are two versions of ACS, a unix version (software only) and a windows version (software only or appliance).
If you're running the unix version then the hardware will be Sun as it's only supported on Solaris.
If you're running the windows software-only version then as long as you've got the supported hardware spec then Cisco will support it, no matter who makes the server.
If you're running the windows appliance then there are a least two versions that I know of, the first is the 1111 which is HP (could be a DL-360, not sure) and the second is the 1112/1113 which has Quanta hardware.
Cisco doesn't have an ACS "approved" vendor as such - as long as the hardware meets the minimum spec then it can be supported (subject to contract).
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...