...your card is a PCI-X card and the one your enquirer specifices is a PCI card. Yours is aimed at the higher demands of a server rather than a PC.
PCI-X is generally backward-compatible with most cards based on the PCI 2.x or later standard, meaning that, a PCI-X card can be installed in a PCI slot, provided it has the correct voltage keying for the slot and (if inserting into a 32-bit slot) nothing obstructs the overhanging part of the edge connector. Originally the PCI bus was a 5-volt bus. Later, in PCI Revision 2.x, the PCI bus was a dual-voltage interconnect. In 3.0 this was changed to 3.3 volts only.
It would be up to the buyer to check whether there are any other compatibility issues with the scanner (he doesn't say what SCSI standard it requires) and the MOBO he plans to put it in. I'd refer him to the specs on the Adaptec website and say he needs to decide himself, but it sounds as though your card is over specced for his needs and he could have problems.