Summon Wolf is the basic summon. It requires INT 1. See
here. Anyone can use it if they have INT 1.
Summon DIRE Wolf is a slight stronger version. It requires INT 2, and 6 mana to use. See
here. All classes can use it, if they meet the requirements.
And this is where it gets a little complicated, so please read carefully.
Let's start with mana points.
Click
here to see a break-down of the main screen. You'll note two bars on the upper left. The red one is for your hit-points. The blue one is for your mana points. Note, only mages and clerics get mana points. Warriors and Rogues won't have a blue bar because they don't get mana.
Warriors and Rogues can learn the Advanced Skill Magical Training. See
here for details. That skill lets them use hit-points to pay for the mana cost of an item or scroll. That means they loose life with they use magical items.
So for the scroll Summon DIRE Wolf:
1) Mages and clerics can can cast it rather easily. They just need INT 2, and 6 mana.
2) Rogues and Warriors can cast it with some help. They need to have the Advanced Skill Magical Training, have INT 2, and have enough hitpoints to pay for the scroll (see the details of the skill to see how many hit points it takes to make up for the mana points).
So yeah, all classes can use the scroll, just some require extra work.
You'll come across other scrolls or items that will have mana costs. So keep that in mind before buying them.