1) No, the LaserWriter Pro 810 does not support LN03 printer emulation. LN03 uses Digital's own escape characters. However being a PostScript printer, the LaserWriter Pro 810 can be used in place of many other PostScript printers, including the Digital LN03R, the PostScript version of the LN03. For an application that does not use the PostScript language, the LaserWriter Pro 810 also supports HP LaserJet II emulation.
2) To print to the LaserWriter Pro 810, the output has to be PostScript of HP PCL 4 mode. If you use the LaserWriter Pro 810 with a product such as PATHWORKS, PATHWORKS components will convert VAX text files to PostScript so VAX/VMS users can print their files to the printer. I am not familiar with WPS word processing system, but if it can support PostScript or HP PCL 4 printer, it can print to the LaserWriter Pro 810.
3) If you have PATHWORKS, you just need to define the printer just like any other Apple PostScript printer, and PATHWORKS will set up a print queue to talk to the printer via AppleTalk. Digital has informally tested PATHWORKS 1.2 with the LaserWriter Pro 810 and it worked fine. I would assume Alisa will work the same way.
Even if you don't have PATHWORKS or Alisa, you can still interface to the printer via LAT. This is done by setting up an application port in LATCP and start a queue using the /PROCESSOR=LATSYM. This procedure is fully documented in the Network Installation and Configuration Manual.