Is it worth it to use Great Person's improvement on tiles with ressources?

The reason great person improvements collect strategic resources is because those resources are hidden until the correct tech is researched. Putting an Academy on a tile then being forced to demolish it after discovering it's the only source of oil in the region would be immensely frustrating.

As for whether it's worth it, it's not ideal. Usually you're better off building the improvement somewhere else and the appropriate improvement on the resource- especially for later game strategic resources.

The exception to this is if you urgently need the resource. The great person will make it available instantly while a worker will take several turns.

Note that this only works with strategic resources and does not work with luxuries. Building a great improvement on a luxury resource is just a waste of a luxury.