Does a Tt plant have the same genotype as a TT plant?

Nope! TT is the dominant phenotype (what ever it may be) and tt is the recessive phenotype (what ever that may be).So say T is the allele for Tall plants, t is the allele for short plants. TT would be show the tall phenotype while tt would show the short phenotype. If the genotype was Tt, the phenotype would be tall as well because the T is dominant and masks the phenotype of t (short plants).