I'm not sure I see the problem with either hashtag, to be honest.
If I am a Christian and I use the #PrayForOklahoma hashtag, I'm basically waving a flag that says, "I'm a Christian and I believe in prayer. Therefore, I encourage you all to join me in praying for the victims of this disaster". I would imagine that most people posting that hashtag would then pray for the victims though, perhaps, there are some who promptly forget about the entire thing and don't.
If I'm an atheist and I don't believe in a deity or deities, I think of prayer as effective as sitting around talking to yourself. I, therefore, might choose to create a post with the #ActuallyDoSomethingForOklahoma hashtag. In that case, I'm waving a flag that says, "I don't believe prayer will accomplish anything but there are things we can do that will help". It appears that people who use this hashtag also post links to the Red Cross or other organizations one can donate to who are aiding the victims of the tornado. Yes, some may not actually give any money themselves but, to be fair, not everyone can always afford to give. They are passing on a helpful message for those who might choose to give and I don't think there is anything wrong with that.