Well actually, if I recall correctly Dove said that you would be able to consume both Secundus and Aegis, and potentially some other SoulAllies/Minions as well, but that you would have the choice to consume Aegis and Secundus for the full skill set, only Aegis for one side of it, or only Secundus for the other side of it. I also believe it was stated that you could reverse the decision by "regurgitating" Secundus and Aegis, however all this was stated years ago when we first began talking about ChaosWeaver and FleshWeaver, so plans may have drastically changed since then. I'll try to hunt down the places Dove said all that, but considering they're from over a year and a half ago, I don't think I'll be able to find much.
But for fleshweaver or chaosweaver? because If you are fleshweaver, you cannot consume aegis (secundus it would, but aegis...) because it could hurt him too much. Fleshweavers are so agressive (you can see roirr, secundus could keep, because he is fleshweaver too), also they can whatever soul ally they want, but at a high price. I really don't use it if it can hurt aegis.
Update: I investigated about chaosweaver and i could see the difference and what they are he he he. So... I think if you are chaosweaver, may you can use secundus as a soul ally.