It would be 100% ridiculous for the NBA to block the trade. It's a fair deal; a highly-touted #1 pick for an All-NBA player. Minny's not going to get a better offer for Love; it would be killer to that franchise if the deal was vetoed.
And what's the issue? That Cleveland and Love have more-or-less agreed to a contract extension, before the trade is *officially* completed? Who the **** cares? Boston did that with KG. If Love wasn't being traded, he could be talking extension with Minny. It benefits all three teams to let Cleveland and Love talk; Cleveland gets assurances Love's going to be around, Love gets his contract security, and Minny gets the maximum return on the trade. This hurts no one.
2 things:
1) The CBA has rules. One of them essentially says that you can't do what Cleveland has been reportedly doing with Love, which is get an agreement for a new contract so far in advance. It's been the rule for years, and they care about that rule to the extent the can enforce it.
2) It's not remotely what the C's did with KG. There, KG was signed to an extension as part of the trade, under the rules of the CBA that existed at the time. The Cavs are well within their right to negotiate an extension with Love as part of the trade, but extensions are very limited, and Love's extension would be for this year, next year at his current player option value, and the following year at about $17.5 million. That's the most he can get. That's vastly less than the $120ish million over 5 years if he re-signs with Cleveland for his full Bird rights. If Cleveland agreed to offer Love a max Bird contract next summer and Love agreed to accept it as a condition of this trade going through, that is against both the letter and the spirit of the CBA, and the NBA would be well within their rights to quash the deal. There is a reason Ainge said on at least one occasion that he was willing to trade for a player without any sort of extension in place -- because he knows that extend-and-trade deals are not player friendly, and are designed to nix the type of KG deals we saw in the past CBA. And the team that should complain loudest, much as I hate them, is the Lakers, since they had to trade for Howard with no assurances he'd stay, and then he walked.
I think the extend-and-trade rules of the CBA are stupid, but they're the rules, and if the NBA can get evidence they weren't followed, the trade should either be blocked, or Love should be prevented from re-signing in Cleveland. I doubt the evidence can be gathered, but the League office looks very weak if they can't enforce their CBA amongst their owners. And not following the CBA from the owners side will hurt them in a couple years when they negotiate a new one with the players.