While tumors do thrive in a blood rich environment, the same has not been shown to be true for a oxygen rich environments. No research has shown that hyperbaric chambers increase cancerous growth rates as the treatment only involves increasing dissolved gases in tissues, not regrowing blood vessels in hypoxic areas.
The issue regarding DCA delivery to cancerous tissue is pretty much a non-starter. Due to its relatively small size, DCA is readily absorbed through cell walls so over time it saturates the cells of the body. In small doses, it's completely non-toxic to healthy cells.