Yep, it is. Devil Summoner is a series of SMT games. One of it's many series.

To answer your question [@Notorious Guy], yeah. You can have multiple demons, but not at the start. Throughout the RP, new demons will pop up, they will be ones directly from the SMT series, so no unique designs, and will be stored into Kuda that can be used with your COMP. While most demons will simply cause your form to recolor, there are some demons that are compatible with your contract demon, thereby causing them to fuse and give you a new form when you transform.

You can also summon them normally like you would in Devil Summoner or other SMT games and fight alongside them rather than slotting them in for a transformation by equipping the right modules (see COMP building). 

This is all new to the series, and isn't in any of the games, but if you're a fan of Kamen Rider, you'll be more or less aware of how it works.

It takes place in the same world as Devil Summoner, with more or less the same rules, but leans more on new rules that the setting accelerated into the future provides.

Simply put, it's in the same universe, but I'm doing a lot differently it may as well be completely new, although relevant rules in the original series will continue to apply here.