Can an alpha thalassemia carrier marry a beta thalassemia carrier?

Of course you can. A person can marry anyone they like. From a thalassemia perspective, and assuming your Alpha thal trait is in cis, your child has a 50/50 chance of being Alpha thal trait vs. Normal and a 50/50 chance of being beta thal trait vs. Normal. Given there is consideration of inheriting two distinct trait states, it would be prudent to sit with a genetic counselor to understand the implications clearly.