Even if there IS an NHLPA problem, they can easily compile the teams, but using the players' numbers instead of names.
Madden 2002 has a whole wack of historical teams, the players just don't all have names.
Actually, thinking about this in greater detail, EA just didn't have any idea how to approach animating the players without helmets. From the buzzcuts and grecian formula of the 40s and 50s to the free flowing coifs and lambchop sideburns of the 70s, it's a lot of work!
About the closest there is now is being able to use the original uniforms of teams that relocated. Figures, they don't have the Whalers uniform in there for the toilet bowls(I mean hurricanes ) but it is kinda fun to have something that resembles the Nordiques playing the Jets.
The NHLPA problem is that players which are no longer in the league cease to exist as members of the NHLPA, and therefore EA Sports would have to contact every person they wished to represent individually, and since the contract wouldn't be with one source, it would be cost prohibitive. It's the same reason that there isn't historical players in any NFL games. I have LONG fantasized about playing with Rocket Richaud and Wayne Gretzky on the same line. Playing with Mess in his prime, and that 86 oilers team. The islander teams of the early 80s with all of their incredible talent vs the early 90s canadiens team.