This sounded like a good idea, so I did some testing. Here is what i came up with:
1: Only units with a "pickup" animation can pickup treasures.
2: Simply adding the "Discover" tactic to the units tactics xmb does not work.
3: Only Heros and Explorers have the 'pickup" animation.

Working Fix:
1: Add "Discover" to Scouts Tactics.xmb---
***Open Tactics with AoE3Ed and overwrite xml with this, then save as .xmb ***

<?xml version="1.0" encoding="utf-8"?>

<tactics>
<action>
<name>Discover</name>
<type>Discover</type>
<anim>Pickup</anim>
<maxrange>0.2</maxrange>
<rate type="AbstractNugget">1.0</rate>
</action>
<action>
<name stringid="38134">HandAttack</name>
<type>HandAttack</type>
<maxrange>1.0</maxrange>
<rate type="Unit">1.0 </rate>
<attackaction>1</attackaction>
<handlogic>1</handlogic>
<anim>HandAttack</anim>
<action>Discover</action>

<impacteffect>effects\impacts\melee</impacteffect
</action>
<tactic>
Normal
<action>HandAttack</action>

<attacktype>LogicalTypeHandUnitsAttack</attacktype
<runaway>1</runaway>
<action>Discover</action>
<autoretarget>1</autoretarget>
</tactic>
</tactics>
<impacteffect>effects\impacts\melee</impacteffect
</action>
<tactic>
Normal
<action>HandAttack</action>

<attacktype>LogicalTypeHandUnitsAttack</attacktype
<runaway>1</runaway>
<action>Discover</action>
<autoretarget>1</autoretarget>
</tactic>
</tactics>

2: Change the <AnimFile> in <Unit id ='412' name ='NativeScout'> (in proto.xml) to: <AnimFile>units\spc\kanyenke\spc_kanyenke.xml</AnimFile>

And, there you have it. All Native Scouts will look like Kenyenke, but can now pick up nuggets (Also they only walk rather than running)
You can change a lot of their actions in Proto also; ie. if you want all of Kenyenke's actions added to the Scout, just cut and paste.
Hope this helps.
****Add a > after impacteffect and attacktype lines, the site kept dropping them. ****

Settlers have pickup animations too.

Tnx for research and feedback

hmm .. I was hoping to find a way about techtree. I wanted to create a special HC card which enables nugget claiming.
I did some other tries by adding proto actions but without success. pity ..

Well, unsolved problems don't let me sleep peacefully , so I grabbed it out once more.
Here's now the final solution to let the NativeScout claim treasures.

At first entries in the unit's *.tactics file have to be inserted - here in "scout.tactics"

1) add action description to <tactics>

<action>
<name>Discover</name>
<type>Discover</type>
<maxrange>0.2</maxrange>
<rate type="AbstractNugget">1.0</rate>
<anim>Pickup</anim>
<active>0</active>
</action>

Note: <active>0 is optional => don't enable per default, but later in techtree via "ActionEnable".

2) add for every single <tactic>

<action>Discover</action>

With this modifications on tactics file the action is acknowledged, but not executed if the Pickup anim is missing. Though the pointer changes to treasure symbol, the nugget isn't collected. Replacing Pickup with another anim doesn't work.

3) add anim to corresponding AnimFile. These are usually in art1.bar, here for "units\natives\aymara_scout.xml"

<anim>
Pickup
<assetreference type="GrannyAnim">
<file>animation_library\explorer\pickup_explorer_A< /file>
<tag type="SpecificSoundSet" checkvisible="1" set="GatherFruit">0.35</tag>
</assetreference>
<component>ModelComp</component>
</anim>

Though I tested only with NativeScout, the method should work also with other units. Perhaps the tags <file> and/or <component> have to be adapted.