Treats can be a very important part of training your bunny. Like many pets, bunnies can be motivated by attention and/or food rewards, so using treats can be a great training device.
Any high-sugar treat like fruit should be only a small part of bunnies diet, so moderation is important. It has been recommended that fruit is not more than 10% of a bunnies diet.
Carrots (also high in sugar) are recommended to be not more then 15% of the diet.
For my pets, I try and keep the total of all high-sugar treats to not more then 5%; occasionally days will pass without added sugar. This makes the reward more effective and is better for bunny health.
Depending on metabolism and/or proportionate to veggies, you should be limiting the amount of pellets your bunny receives to 1/4 to 1/2 cup pellets per 6 lbs. (2.7 kg) body weight. Part of this daily pellet allowance can be used as a treat, for general behavior, and for training.
For the big events requiring high motivation, I use raisins. They keep well and are small enough that I can give as many as 3 daily for really difficult challenges.
Your rabbit is very trainable so using a keyword when calling your bunny for a treat can be very rewarding for you both.
When calling them, we use the word "quick" followed by their name. You don't need to have a high-sugar treat every time they come on command. Their being unsure if the reward will be high-sugar, providing a pellet or a pet will increase their responsiveness (this is why gambling can be so addictive).
Remember, no amount of treat will entice a bunny into a situation that makes them feel threatened. Socialization of the bunny and moderation of the visitors behavior are both important parts of the interaction, and it sounds like you are doing a great job making this part of your process.