But it's not clear how many of the immigrants subject to Obama's order will be able to buy—and able to afford—health coverage through their jobs or in the individual health plans, said Samatha Artiga, director of the Disparities Policy Project at the Kaiser Family Foundation.
"We do know, historically, that immigrants have been more likely to have low-wage job and be in industries that do not provide health-care coverage to workers," said Artiga.
And even if they are offered coverage through their employer, "In many cases, that's unaffordable," she said.
Artiga said Obama's order could alleviate the fears of being deported that have kept some of the affected undocumented immigrants from enrolling their U.S.-born children in Medicaid and CHIP health insurance programs that those kids are eligible for due to their citizenship status.
"From past research and experience, that has always been a big barrier for enrolling children in those mixed-status families," she said.
"But I think the broader issue is that individuals remain without access to affordable health coverage options, so many of them may remain uninsured."
But that doesn't mean they will stay out of the hospital.
Uninsured undocumented immigrants, along with other uninsured Americans who visit the emergency room and get other hospital services despite being unable to pay for their care, in 2012 generated nearly $46 billion in uncompensated care costs at 4,999 U.S. hospitals in 2012, the last year data was available, according to the American Hospital Association.
Those costs, equal to 6.1 percent of total hospital expenses, end up being covered by a federally funded program, by extra charges to those with insurance, or by the hospitals themselves.
While the AHA doesn't have data on how much of those costs are due to undocumented immigrants, they can be considerable in individual cases.
Dr. Julia Koehler, a pediatrician at Boston Children's Hospital, told CNBC about how an undocumented Brazilian immigrant had previously sought her help after incurring a back injury he suffered while trying to lift an older, heavier stranger who had slipped and fallen on some ice on a sidewalk.
For more than two weeks the immigrant, a father of three, had avoided going to the doctor because he lacked insurance, said Koehler, a Harvard Medical School assistant professor who volunteers at a clinic that serves immigrants.
"He ended up with an emergent injury to his spinal cord, which was a prolapse of the disc into the spinal canal," Koehler said. When he was properly diagnosed by "an excellent neurosurgeon," Koehler said, the man was told he had more than a 50 percent risk of paralysis.
"He was going to lose control of his feet, his bladder and his bowel, and not be able to work anymore because he didn't have health insurance," Koehler said.
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Fortunately, the man's surgery at Brigham and Women's Hospital in Boston was a success, and he made a full recovery, she said. But the surgery itself cost "tens of thousands of dollars," which he was unable to pay, and which the hospital absorbed.
While the man's story has a happy ending, Koehler said in other cases, breadwinner in immigrant families are hurt on the job or get sick elsewhere, and then are left temporarily or permanently unable to support their families, which can in turn lead to health issues for them as well, and them becoming an economic burden to hospitals and taxpayers.
Even an immigrant going without a flu shot because of lack of insurance can lead to significant costs for others, she said.
"If you don't have health insurance and you have low income, it is very unlikely that you will come up with the money to buy a flu shot," Koehler said. "So the unimmunized person will then possibly expose other vulnerable people, perhaps asthmatics, young infants, older people."
"Health insurance should be available regardless of immigration status, because, again, it goes beyond the health of the affected individuals, and it goes to the health of the whole family and the whole community," she said.