As far as I know, both tools are used for code generation. Libraries generated with t4 can be used everywhere and type providers can only be used with F#, so what is the point?
As @pad said, it is possible to consume F# Type Providers from C# (depending on how you implement your type provider).
IMO, the main benefit of type providers over T4 is that they're distributed as .NET assemblies, which makes it much easier/simpler to use them from multiple projects. AFAIK, T4 requires you to copy (or otherwise include) the macro files into each project you want to use them in. (It's been a few years since I've used T4 though, so it's possible this has changed.)
In general I think that there is a large overlap in functionality between Type Providers and T4; so yes, if you wanted, you could replicate much of the Type Provider functionality with T4. However, the more functional programming you do, the more you'll learn that modularity -- in just the right amounts -- is what makes functional languages much more productive than their imperative bretheren; and for this same reason, the way Type Providers are constructed and the way they integrate with the F# compiler make them better to use in practice than T4 macros.