If you want a badass eidolon, don't go master summoner.
Have it be small size fly spit webs or poison or spells. How about have it stand next to you have a tail slap combat re flexes and psh back. Then just have it smack guys that approach you it doesnt have to hurt them... alot of opossibiities.
Remember your ability to give a lot of summoned creatures orders is limited. In the case of the viper it really isn't useful as a scout at all. (Unless I misunderstood the reason you posted the viper)
If the goal is to make the eidolon a scout do the following. Evolution for ± 8 to a skill skill focus stealth Max ranks small size and use refuse person on him.
Serpentine eidolon will have + 21at lvl 1 and I think 26 with reduce person.
Basically decide do you want a scout, a bodyguard or so me sort of control guy or a mixture if evolution points allow. Although as an aside the level of stealth posted above is way over kill.
It appears where you designate and acts immediately, on your turn. It attacks your opponents to the best of its ability. If you can communicate with the creature, you can direct it not to attack, to attack particular enemies, or to perform other actions.
It's somewhat GM discretion what sort of actions you can instruct a summoned creature to perform if you can communicate with it. (If you can't communicate with it, it's clear that it just attacks your enemies to the best of its ability.) It's up to your DM whether scouting missions of various levels of complexity are within the scope of what a viper is capable of. Note that at the very least you need some kind of magical means to talk to the viper, since it has no languages of its own. Once you can summon elementals (Summon Monster II), you can communicate with those using normal language.
Basically for intelligent stuff you need a language in common. Ex aqua for water elemental. But all of the celestial or fiendish animals are animal intelligence. So the only way to make them do anything other than attack is probly handle animal.
Basically the creatures summoned want to do what you tell them, but if they can't understand you they just attack the enemy. This means planter arch on can be used as scouts vipers not so much.