Can sikhs use saam, daam, dand and bhed?

Notice that the 28th Hukam is "Rajneeti Parni" i.e. learn politics and the 29th Hukam is to use Saam, Daam, Dand and Bhed to win the enemy. These can be explained as follows:

1. Saam - Try to have a conciliatory approach towards the enemy to pacify him and end the enmity.
2. Daam - If Saam does not work then use Daam i.e. money to win over your enemy. In today's society, this could mean giving aid to the enemy country or having a heavy trade agreement with the enemy 

country which many times ends the enmity because economic concerns motivate both countries to keep peace and ignore hostilities.
3. Dand - If both Saam and Daam don't work, then use Dand i.e. punishment or force to pacify the enemy.
4. Bhed - If Dand also does not work, then use the last weapon i.e. divide the enemy. This is when the intelligence agencies like RAW, CIA, ISI, MOSSAD etc. come in play. They do clandestine activities in the enemy state and divide the enemy. Once the enemy becomes disunited, it becomes weak and thus becomes susceptible to defeat. At this point Dand tactic is used to suppress the enemy.

About Rajneeti (politics) there is only one main book in India - Chanakya Neeti and Siri Guru Gobind Singh jee Maharaj had this book translated from Sanskrit to easy Punjabi/Hindi, by one of the 52 scholars of Guru Sahib's Darbar. I believe Kavi Sainapat translated this work. All the contents of this book are not in accordance to Gurmat, and as such should not be adopted but reading this book does make you street-smart.

At worldly level, even a Khalsa state would have to employ these tactics (Saam, Daam, Dand, Bhed) to secure its borders but at personal level, a Gursikh would stay away from these political tactics and rely solely on Akal Purakh for security. This does not mean that wisdom should be discarded but its best to never have such an enemy, towards whom, you have to employ these tactics. There is nothing like a peaceful life. Most of the times, Khalsa relies on Siri Akal Purakh and Siri Sahib for security.

As for these Hukams being authentic, they are recorded by Maha Kavi Santokh Singh. These must have been alive as oral tradition within Khalsa and he did the Seva of recording these Hukams. All Hukams that are in accordance to Gurmat, should be adopted.