Yeah, this.
Tom's endorsement aside, some caution is still warranted in how you approach this topic IG as there are circumstances that could crop up around this that might lead to a related violation if you aren't careful. Use common sense and do not exclude people against their wishes.
For example, (I presume) it is okay to remove (if the lord actually does it) less active characters from that army, so long as they receive no other retribution for it. That is, even with the understanding that it is an activity-based army, it is still the player's right to miss a turn or several... So he does not meet the standard for the army, but that is not dishonorable or whatever other consequence. (Kind of like being in a cavalry army and recruiting a MI unit on the refit.)
