Is crowd tactics useful to arnold?

This answer will not be too definitive, but I still hope my thoughts aid you a bit

Arnold is an AF general, but not one that must be deployed immediately like Dowding, who, in both campaign and conquests, can only really use AF in early rounds (missile use extends a bit longer) because he must stay far from combat.

So, Arnold can indeed be used more aggressively (and I am sorry to say I have never used him this way), but one must consider the opportunity cost of doing so. Unlike aura boosts in EW6, crowd tactics only work on units immediately beside the general, so to use the skill you might have to deploy Arnold where his main use, AF, becomes less effective.

For example, in the fastest speedruns in the game, 1939 and 43’ USSR, I used Arnold on Tokyo to save money on AF (more danger = less money needed to spend on it). If he was deployed earlier than round 8/9/10 when I did MAYBE another Manchurian or Korean city could be captured faster, but this risks him not being available on Tokyo where the level 3 airport is necessary.

Frankly, this is the only situation in conquest I can think of where it is even possible to use his CT, so let me know of any potential uses you are thinking of. In 1950 and 80’ speedruns the path of friendly units is not at all where AF is needed, so there really is no argument. This more generally demonstrates the role of AF in WC4, which is to attack regions land units cannot get to fast enough.

Hope I helped!