No.
you can't battle any of the gym leaders anymore.
There are 8 gym leaders in Pokemon lake.
one of the gym leaders give you it
the only problem is you cannot catch a gym leaders Pokemon !!!!
There are different types of gym leaders and each gym leader has a different pokemon type.
You cannot rebattle Gym Leaders.
Its always good to have a range of diiferent type Pokemon. If you have any Pokemon that the gym leaders Pokemon are weak to then you should use them.
No, however, in Pokemon Platinum, it is possible to rebattle gym leaders at the Survival Area.
you capture the ledgon dariy Pokemon
I have competed the entire game at least 3 times and there is no possible way to re-battle any of the gym leaders
the people give you hints to find gym leaders.
Yes. After you enter the fighting dojo in saffron city you can find gym leaders and ask for their cell numbers or someone else will give it to you.