It is highly unlikely that the license you purchase that way would be valid. Your software would still technically be unlicensed if you are concerned about staying legal and above board. Some companies care more about this than others, but just because they don't jump on you it doesn't make it legal.

Is it morally acceptable? Entirely down to the individual to make that call.

Practically, you may find that you cannot obtain support, patches or upgrades, etc. I am not familiar with how that software works but some companies require you to register an account with them (providing license details as part of the process) before you can get support.

If there are any purchasing problems, you have less (or less easily obtained) legal recourse if the seller doesn't want to play nice.

The seller also may not sell it to you, as doing so would undoubtedly be in breach of their distribution contract with the original company.

These are a few of the possible pitfalls. It's not advice either way as to what you should do :)