I don't know much about this but I'll use my experience playing Empire at War to judge the outcome.
Firstly, does Rieekan have Snowspeeders? Because if he doesn't then he's at a severe disadvantage. Rieekan has MPTLs, which in any other confrontation would tear through Blizzard Force with ease. However Veers has 9 AT-ATs with powerful, long range fire capablities, and extremely effective against MPTLs - as soon as the proton torperdo launchers enter the battlefield, the AT-ATs will quickly target them and rip them to pieces. We also have to consider the fact that Blizzard Force can take over enemy trenches as so protect themselves against attack, however they'll be pretty defenceless out in the open.
Nonetheless those AT-ATs are going to do some heavy damage, if I were in Veers position I'd take out the MPTLs first then move on to the other tank units, and have my walkers and the like engage the enemies walkers. With the tanks eliminated, Rieekan would be at a major disadvantage and his walkers would be severly outnumbered and be quickly destroyed. Then its just a case of taking out his ground forces, laying waste to his shield generator and razing his base.
Yes he does, Rieekan has Echo Base entirely and all its resources, and again...Veers just has Blizzard Force, so no orbital bombardments or TIEs or anything of that nature.