The following excerpt from the link below and associated RFC2401 does indicate TOS values are preserved when IPSEC tunnel mode is used.

http://www.cisco.com/warp/public/105/crypto_qos.html#t4

Cisco IOS Software Release 11.3T introduced support for IPSec and along with it the ToS byte preservation feature. With this feature, the router automatically copies the ToS header value from the original IP packet to the encapsulating IP header when the IPSec in tunnel mode is used.

Cisco PIX Firewall version 5.1 and later and VPN 3000 Series Concentrator version 3.5 and later support ToS byte copying. Section 5.1.2, "Header Construction for Tunnel Mode," in RFC 2401 mandates copying the IP ToS bits.

ToS byte preservation also applies to AH. Also note that ESP in transport mode retains the original IP header, and the original ToS value is transmitted even without ToS byte preservation.

If packets arrive at the router without a set IP precedence or DSCP values, you can mark based on class to remark the packet headers before encryption or encapsulation. When the packets reach the egress interface, the QoS output policy can then match and act on the remarked values.

http://www.ietf.org/rfc/rfc2401.txt?number=2401

HTH

Sundar