Am I missing something with Gilles De Rais?

[Kaptain O]

He gives me 24 points to spend on additional troops that come in after the battle starts but as he is a Merc Officer, without "Prestige" and since there are no Independent Mercs with Prestige  these models would have to be Mercs.

This pretty much limits him to:

1 Lemure Smuggler guy
1 Bounty Hunter
2 Deserters
2 Damned Rank and File
2 Lost Nomad guys (seems bad because these guys only abilities are scout/first contact which comes into play prior to them being added to your army).

Is there some way Gilles can access models from another list that I am not thinking of?

[Jens]

That's pretty much it - nonetheless it can be quite valuable, e.g. the Lemure Smuggler is a pretty strong counter to other infernalist and can become most handy if your opponent should play Assaliah or something, but he can be almost useless against some other armies (he has some limited use if you want to burn CMD points of the opponent if you run Alazais along) and for objectives it might be useful to have the rather fast Nomad guys in some encounters.

[Liancour]

You're right. But it gives Gilles several advantages.
As you chose your reinforcement after deploiement, you got an idea of your opponent is playing, and therefor what coulb be interesting to counter him. If he plays an infernalist, Angelo could be a good idea, if the scenario is some knd of scavenging nomads can help you (even if you cannot benefit of some special abilities) and anyway, Helle Moller is always a good choice.
Keep also in mind they can be brought by any edge of the battlefield, and that's also pretty interesting in a lot of scenarios.

[Kaptain O]

Yup, it's better than nothing for sure and has it's uses, I was just hoping for someway to open up access to more models.

The Gilles model is fantastic and I must have him, but I don't have any Mercs to go with him currently.

[Balgin]

Helle Moller is always a good choice.

The fact that she used to come in the box with Gilles de Rais and cost most, if not all, of his 26 point bonus allowance pretty much implied that the extra points were just there so you could always have her along with him whatever his actual list was.