I think to achieve its goal, the mad scientist would have created a new chromosome, H, to replace the X and Y chromosome. The H chromosome would provide most of the same genes as the X chromosome, allowing the bearer to live with an H instead of one or more X chromosomes.
One difficulty of producing functional simultaneous human hermaphrodites is that the female hormones (progesterone and estrogen) and the male hormones (testosterone) tend to interfere with one another. Even if an individual had both sets of genitalia, only one set could be functional. This new H chromosome would produce a new hormone, which I'll dub "androsterone". Androsterone would promote both male and female sexual traits, and would allow both types of genetalia to be funcitonal.
Depending on the details, the H could be incompatible with the X or Y chromosomes (inability to breed with standard humans) or it could dominate/partially dominate the X and Y chromosomes. It could be that HX and HY individuals would be sexually dimorphic (but still hermaphrodites), while HH would tend to be more androgynous.
Injecting this genetic change into existing adults and children will not cause them to suddenly sprout new genetalia; those grow in the womb. For the purpose of the story, the genetic change would probably cause the bodies to start producing androsterone. As the normal human hormones flushed from their systems to be replaced by androsterone, secondary sexual characteristics (breasts, beards, etc.) would start to emerge.
The next generation of people would all be hermaphrodites. Since they would all be HH, they would not be sexually dimorphic. Though, there could be variations on the H chromosome that lead to some level of dimorphism. Maybe there are two versions of the relevant genes, H and h, where HH tends to present as more female and hh as more male, though both combinations would still yield hermaphrodites. There are various modes of dominance, so Hh could be more androgynous, more one gender or the other, or in each individual, one could dominate (I believe that in women with two X chromosomes, one tends to completely dominate the other).
So, to explicitly answer the question: "Would there still be dimorphism?": The answer would be: "It could go either way, depending on the exact nature of the change."