For the Celestial Hurricanum it says under its special rule; Portents of Battle: "The Hurricanum and all friendly units within 6" have a +1 bonus To Hit in close combat" as written. I believe this stacks with other Celestial Hurricanums as it refers to "THE Hurricanum" as in "This 1 confers..."
If they didn't wish for this to stack I'm positive they would have written similar to its Locus of Azyre rule or purposefully mentioned its innability to stack as they have for all the other effects found in the rulebook. If it shouldn't be stacked it would be written "All friendly units within 6" of 1 or more Hurricanums..." which would not be too far different from its other special rule Locus of Azyr which specifically says "If you have 1 or more hurricanums on the battlefield at the start of your magic phase, add 1 dice to your power pool."
Some might argue letter over Spirit and I can't help but read the last paragraph of its fluff saying "(within the presence of it) They (empire soldiers) are able to predict the actions of the foe with uncanny accuracy, and know exactly where and when to strike a critical blow." In my eyes having 2 Celestial Hurricanums effecting the same unit would help to focus those predictions.
Also, i fully am aware that 1's still always fail when rolling to hit =P