There are so many environmental factors (stress, feed, weather...) that can contribute to a vitamin deficiency, and Thiamine seems to be one of the most common and is very serious. The ataxia and lethargic behavior makes me wonder, and now that you mention blood around his antler base, could this be head trauma? Any chance he has been fighting through a fence, or has wacked himself on something? What had you thinking pneumonia? Is he respiratory/snotty, or did the other behavior just lead you to think he was sick, and it is pneumonia season so seemed like a reasonable guess? Have you taken his temp? Assuming he is a mature buck, weighing over 100 lbs, the 14 oz of fluid you gave him isn't enough to prevent dehydration. You would have to run at least 1 liter of lactated ringers subcu. daily until you see him drinking regularly. Try to notice his urine, it will be dark yellow and pungent if he is becoming dehydrated. I am a big fan of heat lamps and warm/dry bedding. If he will tolerate the confinement, stick with it. Is he eating at all? You just have to balance the good you are trying to do with the amount of stress it puts him under. We can shoot ourselves in the foot pretty easily if all our efforts are being undermined by the stress we unintentionally impose. Such a difficult balance to try and achieve.
Good luck.
Brett - thank you!