What type of UPN/WB in HD are you referring to? If you're talking locals (LIL), it depends on the market. Whenever Little Rock gets HD LIL, the local UPN/CW station (the second OTA HD station on the market, after its sister the Fox affiliate) is almost certain to be there; but WB/MNTV isn't on OTA HD yet. But in Cincinnati (I know this because its CW affiliation was announced the same day as Little Rock), CW will be an OTA subchannel of the CBS affiliate, so unless they offer an HD feed to cable and/or satellite, it will never be HD.
If you're referring to HD superstations, or to HD versions of the out-of-market UPN/WB stations (Miami, San Diego, etc.) now being included with LIL in DMAs without UPN or WB, that's E*'s call.