EPIC VASSAL - how to run with less than 8 players?

Is it possible to run the Epic VASSAL mod with less than 8 players? How do you do so?

Yes.

Each player chooses a unique Hand Window (e.g. French, or French Left, or Allied Centre).
It actually isn't technically necessary to match to the Hand Window to the player's controlled units, though it obviously helps to remember.
Each player can see only 1 Player Hand Window (except in Solitaire mode)

So for instance with a 4 player game, you could have French Left & Right, vs Allied & Allied Centre. Since each player "plays" one from the CinC, the actual designations matter little.
In a 6 player game it is probably better if the is French & Allied Left, Centre and Right Hand owners.

2 player EPIC runs much like normal games, a French and a Allied player.

Suppose you wanted 2 French players. One CiC and Center, one Left and Right. Would they both join the game as 'French'? If the Left-Right player joins as one of the positions, they can't see both hands. VASSAL will be OK with 2 players playing as 'French'?

One would join as French (usually the CinC), and the other could join as French Left, or French Centre or French Right. Both players can't occupy the same Player ID.
Only the CinC would have cards in this version (under the EPIC rules). VASSAL would allow both players to have cards in their hand, but not see the other hand.

You need to experiment here.. just start a game offline and join as various positions and retire to other positions. It will very quickly become obvious how it works.