Thanks for your question. Your tree expert is very likely to have seen whether or not serviceberries are thriving in this region, so I would take those observations into account. It doesn't mean you can't plant one but it might need a little more care to help it cope with hot summers (e.g., increased watering, mulching)--especially if you plan to plant it in full sun--since they tend to do better with a bit more shade during the hottest hours of the day.

Temperature trends can help explain why the tree expert might be seeing them struggle with DC heat. Serviceberries are generally grown in USDA zones 4-9 depending on the variety. The USDA Plant Hardiness Zone Map (https://planthardiness.ars.usda.gov/) is the standard by which you can determine which perennial plants are most likely to thrive at a location based on average coldest winter temperatures. DC is currently on the warmer end of that spectrum, split across zone 7b and 8a. To give you some context, 10 years ago the parts of DC that are now in zone 8a were listed zone 7a, which means that the average coldest winter temperature has increased by about 5 to 10 degrees in the past decade. Serviceberries actually need a certain number of chill hours (temperatures below 45°) in order to properly set fruit. If tempertures continue to trend upward, the serviceberry may experience heat stress in the summer, and reduced fruit production. Again, this doesn't mean you can't plant it, just that it may need more care as it gets established and when temperatures are very hot. 

Some other shorter native trees/shrubs that you might look into are eastern redbud (Cercis canadensis), crepe myrtle (Lagerstroemia), fringe tree (Chionanthus virginicus). 

Hope that helps, and please reach out if you have additional questions. 

You're welcome! The serviceberry is definitely a beautiful option. You can find some additional information about caring for a new serviceberry tree here: https://piedmontmastergardeners.org/article/serviceberry/

Happy planting!