I think it is almost impossible with just dolphins, too many to coordinate and the total power of dolphins might not be enough. We have 1807 dolphins (not sure how many are still active though) with power of 6,193 to 61,860, if we are generous and give them an average power of 30,000 we would get 54,210,000 HP if all dolphins vote... Not sure about 30K average as there are 1,174 of less than 30K and 633 of more than 30K, but if this block includes some Orcas and Whales it might be possible :)

Hive is not very decentralized take a look at these numbers 53 accounts hold 51% of all staked Hive:

These top 6 hold more HP than all dolphins combined:

And I am one of those dolphins at 48K I am ranked at 437 out of 1,188,377 total accounts that have staked Hive...