When a DER format RSA private key is extracted from an encrypted PEM file, is it still encrypted?
No, it will output the PKCS#1 compatible encoding of the private key, try this:

openssl asn1parse -inform DER -in sample.prv.der


it will output an ASN.1 sequence of:


a version number (00);
the modulus;
the public exponent;
the private exponent;
the CRT parameters.


It did ask you for the password, right?