Can MSDN subscribers apply their credit towards this service?
Azure DevOps is free for teams of up to five users. It's also effectively free for open source use by teams of any size. Larger teams working on private projects would need to be on one of the paid tiers and can't use the free Azure credits to pay for that.
However, Visual Studio subscribers do get licenses for Azure DevOps. If you're a Visual Studio Professional subscriber, then you get a Basic license for Azure DevOps. You get additional benefits if you're a Visual Studio Enterprise subscriber. You can find the details at https://docs.microsoft.com/en-us/visualstudio/subscriptions/...