Homologation (from the verb homologate, meaning "to approve or confirm officially") is the process of certifying or approving a product to indicate that it meets regulatory standards and specifications, such as safety and technical requirements. This happens for every game released in any meaningful jurisdiction. If a game is changed, then the level of homologation depends on the level of change. For example, when you submit a game to GLI or NMI for testing, they normally give you a list of "critical files" - these are nearly always to do with the maths / game logic, which are the bits of the code which are to do with the way the game plays, an achieves it's RTP. If any of these critical files change, then the whole maths would have to be retested. If not, then a code diff would be done on the critical files just to make sure, and then the rest of the game tested as necessary.
Therefore, changing the maths when you convert from Flash to HTML5 would mean that the testing became longer and more expensive - and unless the name is new, or performing really badly, there would be almost no commercial reason to do it.... hence i doubt (and NetEnt have also confirmed) that they changed any of the maths.
That said, the algorithm on DoA that displays symbols that don't land in view is blatantly different on HTML5 DoA vs Flash, so God knows what they did on that but it definitely is wrong & badly implemented.