Is the extension compatible with MultiSafepay?

Yes. Please use the following workaround when installing Fooman Surcharge:

1. In: /app/code/community/Mage/Msp/Model/Payment.php find: //End shipping line item 

2. Add this straight after it: 

if ($this->getOrder()->getFoomanSurchargeAmount() != 0) {
     $surcharge_amount_final = number_format(
        $this->getOrder()->getBaseFoomanSurchargeAmount() + $this->getOrder()->getBaseFoomanSurchargeTaxAmount(), 4, '.', ''
     );
     $c_item = new MspItem(
        $this->getOrder()->getFoomanSurchargeDescription(), 
        $this->getOrder()->getFoomanSurchargeDescription(), 
        1,
        $surcharge_amount_final,
        'KG',
        0
     );
     $c_item->SetMerchantItemId('Surcharge');
     $surcharge_tax_id = 'none';
     if ($this->getOrder()->getBaseFoomanSurchargeTaxAmount()) {
         $surcharge_tax_id = $shipping_tax_id; //uses the same as shipping adjust if necessary
     }
     $c_item->SetTaxTableSelector($surcharge_tax_id);
     $this->api->cart->AddItem($c_item);
 }