Unless Dish has changed their business rules:
It has been the policy of Dish to require ALL used DVR's to be returned for exchange BEFORE redeployment (doesn't matter if you own it). The reasoning is that if there are any movies on the hard drive, then reselling the unit would constitute resale of copyrighted material with-out express written consent of the copyright holder.
I thought the movies on any Dish DVR were encrypted with a key unique to owning account and would not be accessible once that account was de-activated because the encryption key would be destroyed. Sale of an encrypted copy that cannot be decrypted is should not be resale of copyrighted material, if it is why encrypt at all?
I think it depends. I know that all the programs on the EHD are encrypted like that, including OTA recordings which everybody records just fine using other types of DVRs. But the programs recorded on the internal disk may or may not be encrypted. I haven't looked to see if this is still true for a Hopper. But in the VIP days, you could in fact play internal recordings, even if they came from somebody else's account.
I think I know the answer to this, at least from my experience. Last year, I transferred a used purchased Hopper Duo from my old Dish account to the account I am currently using. Earlier this month, I activated a used Hopper 3 that I purchased from another member here, on my same Dish account that previously had the Hopper Duo. In both cases, recordings on the internal hard drive made while the receiver was still on another account will still play just fine. The trade-off is that Dish placed a "D" code on my account to remove DVR functions. This means that there is no way to pause the recordings, nor skip back, rewind, skip forward, fast forward, etc. The DVR's also will not make any new recordings while they are active on my account. The plus side is that I do not get a charged a DVR fee, though.
(Interestingly, DVR functions still work for OTA channels while the receiver is
deactivated. Also, PTAT attempts to record on the Hopper 3 as soon as I deactivate it. Of course, at that point, I am no longer actually receiving the channels, so nothing playable actually records in that case.)
I also have experience transferring ViP DVR's from one account to another. One time, I transferred one of my used purchased ViP612's to another account for my sister to use. As TheKrell said, recordings made while the ViP612 was still on the old account continued to play just fine. In this case, full DVR functionality also continued to work, both for existing recordings (on the internal hard drive) and new ones.