Yes,

The methods of warfare and traditions of the Aztecs, as well as many of the natives were very different from the European traditions. Firstly, they did not battle for total conquest and destruction of the enemy. For them battle and war were relatively ritualized, and the 'cruelties of war' for which they are remembered were strictly controlled and organized sacrificial ceremonies.

For example, when the Cortez's troops who were stationed in Tenochtitlan massacre Aztec nobility when they are gathered in a Temple for celebrations, in 1520. The Aztec's were caught entirely unawares by this. For them, any attack upon unarmored warriors was unnatural and exceedingly cruel. This is one of the main triggers for a wide revolt and resistance against the Conquistadors under Cortez.

        Now onto your actual question ---

When Cortez returned to Tenochtitlan following this massacre, he and his military advisers quickly realized they needed to leave for good. Montezuma no longer held sufficient power over his people and the bridges which surround the city were removed, trapping the Spanish with their allies.

When Cortez and his troops planned their retreat in a very hasty manner, they failed to fully inform Spaniards located in another part of the city. This group of around 270 men failed to make a move on the night that Cortez and his army attempted to escape the city. This unit was sealed in their positions, starved, and eventually captured. Some of whom were sacrificed to the Aztec gods.

This is just one example of the Spanish men being taken captive.

What you must remember is that the Spanish were not as effective against the Natives as they themselves said they were. The Natives quickly adopted to their tactics - ducking when cannons were fired, using successful ambush tactics, using their superior numerical advantages etc.

The Spanish themselves adopted Indian weaponry and armor at times. The heavy metal plates were cumbersome, and cannons/guns not entirely effective in close combat. Cavalry was in very low numbers as well. When Cortez would write and ask for supplies - he would ask for crossbows, bolts and horses first, and munitions were of only secondary importance. They were extremely vulnerable to the numerically superior Natives, if they were not being supported by some of their Native allies. In Jeremy Black's War in the Early Modern World very convincing argument is made that the Spanish were only successful because of the Native allies, and the fact that the Natives used them for their own advantage. In that book he also mentions multiple other points at which the Spanish are captured and sacrificed. However, mostly the Spaniards were lucky enough to die on the battle field.

Sources -

Michael Wood - Conquistadors

Jeremy Black - War in the Early Modern World

Currently taking a degree in history - one of the modules is about colonization, including Spanish America.

Spanish captives were treated just like any other captives, which meant that, yes, they were eligible to be sacrificed. The difference was that the Spanish captives, as part of the invading group, were basically priority candidates.

This was in accord with the political aspect of Aztec sacrifice; it was not only a religious ritual, but the deaths of captured soldiers sent a powerful message to those standing in opposition to the Aztecs. With the Spanish, those intimidation tactics were even more explicit. Following a fight on the causeways into Tenochtitlan, for instance, Díaz del Castillo writes the Spanish:

saw advancing against us with loud yells very many squadrons of Mexicans with very handsome ensigns and plumes, and they cast in front of us five heads streaming with blood which they had just cut off the men they had captured from Cortés, and they cried, "Thus will we kill you all as we have killed Malinche and Sandoval, and all whom they had brought with them, and these are their heads and by them you may know them well."

Now, Malinche and Sandoval had not actually been killed, but the heads rattled the Spanish enough that they were driven off the causeway in defeat. Later than night Díaz del Castillo writes the allied Spanish/Native troops heard drums, horns, and whistles -- the sounds of 10 Spanish (no mention of how many Natives) being more formally sacrificed.

Díaz del Castillo would later write in greater detail about Spanish being sacrificed as /u/snickeringshadow recounts. A little too much detail actually, since he reported seeing things there were no physical way he could have witnesses. It is possible that he was elaborating on what little he could see using accounts of others or events he had seen prior to the war. What happened next though, is supported by various sources. To use Díaz del Castillo's account again:

There was another thing Guatemoc ordered be done when he won that victory, he sent to all the towns of our allies and friends and to their relations, the hands and feet of our soldiers and the flayed faces with the beards, and the heads of the horses that they had killed...

The usual route of inviting opposing leaders to Tenochtitlan to witness sacrifices, both due to the on-going war and the Spanish not knowing how things worked in Mesoamerica, the Mexica opted for a more pro-active method of displaying their dominance.