I am using an impedance meter to measure impedance in complex form (R-jX) and an RLC meter to measure R & C values in an RC circuit. The value of DC resistance is equal to the R value in impedance equation. My question is whether the R in impedance an ac or dc resistance?
It's the real part of the impedance at whatever frequency you're calculating the impedance for.
Very often, the \$X\$ component will be proportional to frequency so that in the limit as \$\omega\to 0\$, the impedance is \$R\$ making \$R\$ the DC resistance.
In other cases, \$R\$ also has some frequency dependence. Then the DC resistance is whatever value \$R\$ has when the frequency is 0.