Forum adverts like this one are shown to any user who is not logged in. Join us by filling out a tiny 3 field form and you will get your own, free, dakka user account which gives a good range of benefits to you: No adverts like this in the forums anymore. Times and dates in your local timezone. Full tracking of what you have read so you can skip to your first unread post, easily see what has changed since you last logged in, and easily see what is new at a glance. Email notifications for threads you want to watch closely. Being a part of the oldest wargaming community on the net. If you are already a member then feel free to login now.

tl;dr Given the fact that Summoning has a 12" range, excepting special circumstances involving movement outside of the movement phase (Running, Assaulting, etc.) there is a 11/36 (odds of rolling at least one 1 on two d6) chance that your summoned unit or the summoning unit will do nothing for the next turn. This goes at least some way to address both issues of balance and issues of Imperial forces being "ok" with the summoning of daemons. Whether it goes far enough is left as an exercise for the forum.

The allies section (p.126) states that "Irrespective of the method you use to choose your army, this section tells you how models from different Factions fight alongside one another" (emphasis mine)

The rules for a Conjuration (p. 26) state "the new unit is under your control and treated as having arrived from Reserves for all rules purposes." N.B. there is no reference to the unit being "friendly", or anything that would overrule the Allies matrix.

The rules for Malefic Daemonology (p. 195) state, for an example of the Primaris Power Summoning "Rules for these units can be found in Codex: Chaos Daemons."

The rules for Factions (p. 118) state "In the case of older publications, the Faction of all units described in a codex is the same as the codex's title.", as well as (above) reaffirming that Faction rules hold "regardless of how you choose your army" (emphasis not mine), which is genral enough to include units summoned by conjuration.

Finally, allied daemons have the "One Eye Open" special rule.

(I hope this argument is easy to follow!)