Defender Isaacs and midfielder Hartog were released by Royal Eagles and Ajax in the off-season.
Santos chairman Goolam Allie says a decision is yet to be made regarding signing the experienced pair.
"Yes, Hartog arrived a few days ago while Isaacs joined us today," Allie tells KickOff.com.
"One cannot shy away from the fact that they will bring a wealth of experience to the squad. They are very professional and know what is required in the modern game.
"We also need to determine how they will impact and add to the balance and depth of the squad - but it's still early days.
"They shall, however, also be put through their paces as well. The coach (Zeca Marques) is still busy with pre-season preparations and needs to finalise the squad."