Yeah the book has a chart for each army relating to the monsters and they come under 3 categories
Kinship - Have as many as you like within your magic and monsters limit
Scroll of binding - follow the scroll binding rules
Abhorrent - only 1 allowed with scrolls
So i am thnking that monsters with 'kinship' are allowed with your army, but not sure about the rest (as no use of scrolls) or just use any as to add a bit of flavour to your army? (although adhering to your army flavour, etc.. i wouldn't use a rat monster in my empire army )
And use as a rare selection or as an addition to your army (so a 1500 point army could have 1100 points from the army book and a 400 point additional monster (as ally) ...
not sure what would work., but reading the rules, seems i can use a dragon with my Dwarf army 'Shard Dragon' has kinship with them....
Automatically Appended Next Post: Ok, after discussing it with the manager and staff, here's how my local
GW store advised to handle it with regards to normal games not using bound scrolls.
Using the Monster/Army table at the back of the Monstrous Arcanum book...
Monsters with the
'Kinship' rule to your army = Count as
rare choice and can have as many as you want (providing you have the rare points available).
Monsters with the
'bound' rule to your army= Allowed only 1 as a
rare choice.
Monsters with the
'Abhorrent' rule to your army = not allowed in your army.
same rules for large units (such as wolf rats/Fimir warriors) but regarded as 'special' not 'rare'.
i think these rules work pretty well and allow plenty of monsrtous freedom

(looking forward to adding a shard dragon or warpfire dragon to my Lizardmen army)