Any plant can cause problems because it may have been treated with chemical fertilizers, pesticides, fungicides or weed killers so even if it's a non-toxic plant you have to know where it came from and if chemicals were used. "Organic" is another word for manure-based fertilizers so there's a strong risk of parasites from organic plants.
Dragon Slave, even aloe vera has phytochemicals that can cause problems if eaten in excess, it's a potent laxative because it contains high levels of a purgative called aloesin and moderate levels of several other purgatives as well. Aloe-emodin can cause severe immune system reactions similar to anaphylactic shock and is considered an allergy "enabler". Very few creatures are allergic to the aloe-emodin itself but it stimulates immune system over-response to other proteins. Aloe also contains emodin which can also wreak havoc with the immune system, it's both a stimulant and suppressive. Beta-systosterol can cause sterility and increases the risk of eggbinding in gravid females. Chryosophanic acid is a calcium-antagonist that can contribute to MBD problems.
They have to eat a fairly large quantity in order to get enough of the phytochemicals to cause problems but if you leave a plant in a cage you never know if or when the beardie will decide to tear into it.
I've seen beardies who have eaten a lot of aloe vera die of malabsorption syndrome because of the food passing through too quickly and they basically dehydrate and starve to death.
Here's a website where you can look up the chemical activities of aloe and almost any other plant you can imagine:
http://www.ars-grin.gov/duke/