I'm glad he's starting to come around, it will be a slow process and you'll probably see little baby steps every day...Now about the "blood" in his poop, are you sure it was actually blood and not just his urates being stained red? I don't doubt you at all, I just want to make sure because it's not uncommon for their urates to look like they have blood in them when in fact it's due to too much calcium. So if it was only his urate that appeared to have blood in it, then it was most likely due to excess calcium in his urate, and I'd wait for his next bowel movement before rushing to a vet. If the blood was actually in the fecal matter part of his bowel movement, then it may be parasites, or it could just be from straining, like Cooper said...if the blood was in the fecal matter portion of his bowel movement, was it a bright red color, or was it a very dark red color? The difference is that if it was a very bright red blood then that's indicative of "rectal bleeding" (for lack of a better way to describe it) caused by straining, as if it's bright red blood it most likely came from right inside his vent area, where if it was dark red blood in the fecal matter then it may be due to parasites.
The reason I'm trying to get you to be cautious about this is that if a vet does a fecal test and diagnoses a parasite like Coccidia or Pinworms, but it's in a low to moderate count, you probably do not want to treat him with the prescription anti-protozoan medication for the Coccidia or the Panacur for the Pinworms, because #1) Unless they are in high or "too numerous to count" numbers and they aren't causing any symptoms like a lack of appetite, lethargy, etc. (which he already has due to the inadequate
UVB light) then they don't need to be treated, dragons live with low to moderate counts of Coccidia and Pinworms throughout their lives with no issues and they are horribly overmedicated by vets for them, and #2) Putting him on one or more anti-protozoan or anti-parasitic prescription meds right now could really do more harm to him than good. It's going to take a while for him to start to come back from the MBD and get back to normal, and it's not at all uncommon for prescription meds to completely ruin their appetites and make them extremely lethargic, and this causes a downward spiral that is hard for them to come back from sometimes, especially if they are already suffering from MBD. So I'd be very, very cautious about putting him on any meds right now...Just my opinion, but that's a big worry right now when he's just starting to show little signs of improvement.
Honestly, one poop with some blood in it isn't anything to freak out about, I'd wait and look at his next couple of bowel movements to see if their is still blood in them before you go rushing him to a vet, even just the stress of the vet visit could really cause him a lot of issues right now, and hinder his recovery.