Do these smoked ham hocks which contain dextrose, contain gluten?
Dextrose is another name for the sugar glucose.  In the US most powdered dextrose and/or glucose syrups are produced from corn starch, in the UK and other European countries they may be made from wheat or other starchy plant sources.  According to a 2008 study from Finland, even though wheat based glucose syrup was found to contain low amounts of residual gluten, it was tolerated without harmful effect by people with celiac disease.  

Though the ham is not likely advertised as "gluten free", even if there was gluten in the dextrose, the final concentration of gluten in the ham would likely be well below the 20ppm concentration to qualify as such according to the FDA rules.