Originally Posted by Eugenides
Well, likely they aren't debuffing, just my guess. The fact that he "goes after spellcasters first" tells me that they aren't being slippery enough, because as a front-line fighter playing with a DM that like his battlefield control, let me tell you that it is HARD.
My advise? Web. Glitterdust. Grease.
GREASE. THAT REFLEX SAVE OR FALL. Seriously, Grease him repeatedly. he won't get anywhere, but your rogue/shadowdancer should get past it with flying colors and tear the mage a new one. There you go, rogue feel like he has a purpose.
In addition to just pitting him up against spellcasters that make his reflex save sad, fighting in unusual areas can exploit his weaknesses. Swinging blades halls in dungeons, cliffs near chasms, etc. Balance checks, even with a racial bonus, make melee tanks scared. Fight at the top of a waterfall, or a swinging bridge over a canyon.
Also, I'm sure you're beating yourself up over this already right now, but Reincarnate is kinda a terrible / gamebreaking spell. There's a reason Lizardfolk have 2 Humanoid HD and 1 LA; even though it's a bit excessive, these are to counterbalance the numerous strengths and bonuses a lizardfolk gets, especially the massive natural armor and secondary bite attack.
Dragon Disciple is already a strong class with a D12 and numerous stat boosts (if you're keeping core) and although it may seem reasonable to swap out the stat boosts for spellcasting progression, bear in mind that spellcasting, even sorcerer spellcasting, is probably the strongest class feature in the game by a large margin. Even 1/2 spellcasting on a d12 prestige class is pretty strong.
That being said, bear in mind your group chose to make him the front-liner, and his drawbacks (in terms of terrain, reflex, and disables) should serve to make life difficult enough for him that everyone is involved.