It'll sure repel the water.
I'm not a fan of using WD40 on tires. I know a lot of folks do, to each their own.
There are better products available for putting oil back into tires, some made specifically for that purpose, some over the counter stuff.
Our Pink Panther does a good job at rejuvinating dry rubber. Our Pink Panther "Thick Formula" works even better with time.
Over the counter products like Liquid Wrench and PB Blaster will help, although they will also soften (which may or may not be what you are wanting.)