Bad decorations, beautiful venue

Would an outdoor reception be an option with a tent - it may fit your theme better?

I agree with Dierdra about doing everything outside. It fits your theme anyway and avoids all the decor issues. If you expect that people will need to go inside to use the bathroom, etc. you may be able to curtain off a direct path or ask the venue to dim the lights to hide the decor. If you are set on an inside reception and you are set on this theme, I would suggest looking around for other venues that might fit better.

Since there is space to have the reception outside, that's where I would have it. Or if the decorations are removable would the venue be willing to store the decorations somewhere else temporarily?

If you're allowed to move things and promise to put them back, I'd move as much as I could. If not, or if they charge a fee to move it themselves (some places will charge you if YOU move their decor because they could claim you 'broke' something), then it's worth asking about. This might be smart anyway because they may not allow you to touch certain things or decorate over them.

If you are allowed to, you could always add some wreaths to the deer heads to give them that magic forest look, like Alycia said! Or hang some stars from their antlers? There are like... nearly no examples of this online LOL - get creative!