There was x86 emulation on Windows NT, on MIPS, Alpha, and PowerPC — in fact, more than x86 emulation, PC emulation. The operating system itself ran natively, and applications could be built natively as well; but for a non-x86 port to be viable, it had to be able to run existing x86 programs.
The Alpha release of Windows NT was quite famous at the time for using a binary translator rather than a “plain” emulator, FX!32, developed by Digital; it would run x86 programs, keeping track of which parts of the binaries were actually used, and then translate them to Alpha instructions and store them in DLLs which were used the next time the programs were run. FX!32 was described in a fair amount of detail in various publications at the time, see this USENIX paper and this Digital Technical Journal article.
On MIPS and PowerPC (and Alpha for DOS x86 programs),
NTVDM.EXE could emulate a PC as well, using a version of Insignia’s SoftPC (which was common on workstations at the time). This post on Virtually Fun looks at the MIPS version specifically.
The scope of these tools is different: FX!32 translates Win32-on-x86 to Win32-on-Alpha, whereas SoftPC emulates a complete 486-level PC. (Even though Alpha was always 64-bit, publicly-available versions of Windows NT were 32-bit only.)