According to the Appendix, the Ambush/Pigstika action card may be utilized by Orcs and Black Orcs only. Yet both of these creatures have a default stance of Reckless, meaning that they can only use the Pigstika side of the card. When can Reckless creatures use the Conservative side of a card?

As I understand it, what creatures can or cannot use any specific card is only a rough guide for the GM. Lots of creatures can buy extra cards (there are symbols on their creature cards that indicate this) and they could buy the Ambush, or if you as a GM want someone to have the ambush card you can give it to them, just like that. There is also a rule (if I remember correctly) that gives you the oppurtunity to change a creatures stance by using their Cunning points, which further opens up for the use of Ambush. Furthermore you could create a calculating Black Orc-leader by giving him a Conservative stance as a default (and maybe bump a stat or two).

Don't let the suggestions of creatures stop you from using cards, have fun with it and change things around. That way, the players won't know what to expect from certain creatures and it keeps them on their toes. It also gives the different creatures more "character" if you add something of yor own to their abilities, and it will be much more fun to use them as a GM (even if the players might not even notice the changes).