The accents of rank-and-file clone troops are the result of the flash training they undergo. The programs were designed by Jango, and likely feature his voice issuing instructions and commands. All of the clones, including the commandos, went through that basic flash training regime, explaining why even Boss has the basic Jango accent. The commandos develop these different vocal inflections and characteristics based upon their training sergeants who took over to teach them further after completing the flash training. It's noted in the Republic Commando novels that most of Omega Squad have accent patterns closer to Kal Skirata, while Atin, who wasn't trained by Kal but by Walon Vau, has a voice more similar to Boss. The novels also state that it's Sev that most closely associates with Vau, the sergeant in charge of Delta Squad's training, and both have lower voices, generally slower speech patterns, and more deadpan attitudes. I had always assumed, and the Republic Commando novels played with the idea, that the drastically different voices we hear from Delta's different members in the game are an audience-friendly means of expressing the more subtle differences in their vocals. Rather than looking at Scorch as sounding exactly like Raphael Sbarge, it's much more likely that he has a lighter vocal tone, a slight grit or rasp, and diction/inflection more similar to Sbarge, while still sounding similar to basic troops to an outside, untrained ear. It's comparable to the trouble many Americans have with distinguishing British accents; is the speaker English, Irish, Scotish, Welsh, or are they actually from Australia or New Zealand? Those who are familiar with the region will be able to place the speaker quickly, while brother clones or familiar Jedi officers have learned to pick up on those differences to a degree that they sound uniquely distinct of one another.