Repro:
1. Pick Tusk and level up Snowball (and get Manta Style)
2. Create an allied Chaos Knight and level up Phantasm
3. Cast Phantasm (and your Manta Style)
4. Cast Snowball on an enemy unit
5. Try to pull the illusions inside your Snowball by right-clicking them
6. Alternatively, try to enter the Snowball with the illusions by selecting them and right-click on the Snowball

Result: Allied illusions can neither be pulled in by Tusk, nor can they manually enter the Snowball. Illusions under Tusk's own control can get pulled in and can manually enter it.

Expected: Allied illusions should be able to enter Snowballs as well. All other non-hero allied units can, and Tusk's own illus can, so there is no reason why allied illus shouldn't be allowed.