I found this website-blog, it has a few more (spoilers) images of the invasion:
【UO】ウルティママニア - livedoor Blog（ブログ）
If the stats
here hold, tamed Dread Horses have:
615 HP
112 STAM
122 INT
534 STR
112 DEX
122 INT
71/20/26/56/40 resists
40/0/0/20/40 damage
20-26 base on hit
No poisoning (---) and no skills above 100 when tamed. I can't translate the possible pack instinct.