7
Yes, it's fine. The mini-DIN PS/2 keyboard interface is electrically identical to the 5-pin DIN AT keyboard interface, so your results will be the same as if the keyboard had its own PS/2 connector.
PS/2-to-USB keyboard adapters vary widely in their behavior, regardless of whether an AT adapter is in play. I suggest looking for models with reviews confirming that they support n-key rollover and BIOS setup screens.
A Soarer's Converter is another option. These are more advanced AT-to-USB keyboard adapters, supporting programmable features like macros and layers. They were designed for an electronics hobbyist to build, but sometimes turn up pre-built in various places online.