One sided approximation degree
I don't think they are polynomially related. Consider the OR function on n bits. There is a polynomial $p(x) = \frac{1}{n} (x_1 + x_2 + \ldots + x_n)$, which approximates it with one sided error $\epsilon = 1- \frac{1}{n}$ because on the all zero input the polynomial is zero, and on any other input its value is between $\frac{1}{n}$ and 1.

However any polynomial approximating the OR function to one sided error $\epsilon/2$ (which is approximately $1/2$) is a bounded-error approximation of OR which is known to require degree $\Omega(\sqrt{n})$.