The answer to the first question is to use pzplot()
H = tf([1 .5],[1 2.5 3.125],1)
pzplot(H)
axis equal
Not sure about the second question. How would the pole-zero diagram be represented in Matlab for input to some function from which the tf is computed? If the poles and zeros are known then
z = -0.5; p = -1.25 + 1j*[1.25 -1.25];
H = zpk(z,p,1,1)
H = tf(H)