Rules As Written, yes. But it seems unintended
Rules As Written yes, the feature states:
The bond with your wildfire spirit enhances your destructive and restorative spells. Whenever you cast a spell that deals fire damage or restores hit points while your wildfire spirit is summoned, roll a d8, and you gain a bonus to one roll of the spell equal to the number rolled. In addition, when you cast a spell with a range other than self, the spell can originate from you or your wildfire spirit.
Strictly just reading this you can add it to any roll of the spell, which would include the attack roll. But remember that this is from Unearthed Arcana and so is not as heavily edited and playtested as other material/rules/features.
Compare it to the the Draconic Sorcerer's Elemental Affinity feature:
Starting at 6th level, when you cast a spell that deals damage of the type associated with your draconic ancestry, you can add your Charisma modifier to one damage roll of that spell.
And then to the Guided Strike feature of the Cleric:
When you make an attack roll, you can use your Channel Divinity to gain a +10 bonus to the roll.
Note that the feature here could not have used either of these wordings as healing spells have neither attack rolls nor damage rolls. It seems likely (and balanced) that this would add to either the damage roll or the healing roll, especially because things are explicit when they can be used to add to an attack roll, such as Bardic Inspiration:
Once within the next 10 minutes, the creature can roll the die and add the number rolled to one ability check, attack roll, or saving throw it makes.
As user @RyanThompson pointed out there is the Alchemical Mastery UA feature of the Revised Artificer which is an example of wording that does apply to only healing and damage rolls:
When you cast a spell using your alchemist's supplies as the spellcasting focus, you gain a bonus to one roll of the spell. That roll must restore hit points or be a damage roll that deals acid or poison damage, and the bonus equals your Intelligence modifier (minimum of +1).