I think as long as you keep it in the normal range (2-3 cups a day) you should be fine, especially since its black and not that starbucks crap. Most people worry about it lowering your insulin but since you exercising you shouldn't have to worry about that. In my opinion both of the guys you reference are right because the caffeine will give you some energy for your workout and help your diet because it has a positive metabolic effect. I use to drink coffee but switched away from it, when I need a caffine boost I use green tea now.

Here are two articles on coffee for you:

Article #1:

Caffeine boosts fat metabolism and stamina in athletes.

by Paul Cribb, B.H.Sci HMS
AST Director of Research

Drinking a cup of coffee before exercise could help increase the amount of fat utilized during the activity, say researchers in Australia.

The team at the Australian Institute of Sport in Canberra also found that athletes who consumed a small dose of caffeine before exercise (approx 200miligrams) could continue to exercise at a high capacity for up to 30% longer than those who had not taken the stimulant. The caffeine supplement enabled the athletes to perform up to 3.5% beyond their normal capacity in a series of performance tests.

The researchers suggested that substances in caffeine triggered the muscles to use fat to fuel exercise instead of the usual carbohydrate stores, thus enabling better endurance performance. In other tests the researchers found that drinking a cola drink or coffee helped cyclists keep going longer than those who were given caffeine-free beverages. The athletes in this study were low caffeine consumers – 1 or 2 cups of coffee a day.

Caffeine can delay the onset of fatigue by up to 60%. However, keeping habitual caffeine consumption to a minimum appears to be important to obtaining its performance enhancing effects. However, no research has investigated the effect of habitual caffeine consumption on fat-utilization. In other words, caffeine’s fat-burning effects may not necessarily be reduced by frequent caffeine consumption.
Caffeine boosts fat metabolism and stamina in athletes.