This is just my theory, but I've yet to see anyone or any evidence to refute it...
BET-J HD doesn't exist- yet. There are several websites that track announced and launched HD channels, and BET-J HD has never been mentioned anywhere. Viacom has never issued a press release announcing it's launch (as they did with Comedy Central). If you do a Google search for the channel, EVERYTHING that comes up is related to DISH. And AVS has recently added it to their channel grid...DISH is the only carrier. Plus, it just doesn't make sense that they would launch BET-J HD BEFORE they launch BET HD.
DISH is essentially just upconverting the standard feed until the HD feed is available. This is what they did with WFN...the first 3 or 4 months of WFN, it was clearly an SD channel (lots of letterboxed programming, but no actual widescreen). After a while, the logo changed form WFN to WFN-HD, and they suddenly had plenty of actual HD programming.
I don't get Platinum anymore...can anyone confirm that the logo NEVER shows "HD" I think that's the proof, as the other Viacom channels have HD logos. from what I've seen.