Are complex number supported by blop?
Yes. In fact, since complex numbers are part of the C++ library, and they are supported by CINT itself, there is no extra effort in blop to add anything to this. However, there are problems with the math functions on complex numbers. You should define them yourself: 
template <class T>
T abs(const complex<T> &a)
{
    return sqrt(a.real()*a.real() + a.imag()*a.imag());
}

template <class T>
T phase(const complex<T> &a)
{
    return atan2(a.imag(), a.real());
}

template <class T>
complex<T> sqrt(const complex<T> &a)
{
    const T amp = abs(a);
    const T pha = phase(a);
    complex<T> result(sqrt(amp)*cos(pha/2),sqrt(amp)*sin(pha/2));
    return result;
}

The script below plots the magnitude and phase of a complex impedance as a function of frequency: 

#include <complex>
double abs(const complex<double> &a) {return sqrt(a.real()*a.real() + a.imag()*a.imag());}

complex<double> Z(double omega)
{
    double R1 = 100;
    double R2 = 50;
    double C  = 0.001;
    complex<double> i(0,1); // imaginary unit

    // R2 connected in parallel with C, and they are connected
    // in serial with R1
    return R1 + 1/(i*omega*C + 1/R2);
}

// return phase in degrees
double phase(double omega)
{
    return atan2(Z(omega).imag(), Z(omega).real()) * 180.0 / 3.1415;
}

// return magnitude
double mag(double omega)
{
    return abs(Z(omega));
}

main()
{
    frame::current().mirror_y1(false).mirror_y2(false);
    frame::current().x1axis()->logscale(true);
    set::x1title("$\\omega$ [Hz]");
    set::y1title("Magnitude [$\\Omega$]");
    set::y2title("Phase [degree]");
    set::x1range(1,1000);
    plot (_1, cfunc(mag)  ).legend("Magnitude (left axis)").lw(5*LW).ac(red);
    mplot(_1, cfunc(phase)).legend("Phase (right axis)").lw(5*LW).ls(dashed).yaxis(axis::y2);
    eps::print("fff.eps");
}