"We speak to them in Spanish."
Translation:Nosotros les hablamos en español.
No, you need an object pronoun in there to define who is receiving the action of the verb.
The 'a ellos' simply defines who the object pronoun is. Les is the indirect object pronoun for 'to them'
You don't even need nosotros. It could be worded:
Les hablamos en espanol a ellos. or
A ellos les hablamos en espanol.
Whichever way you still need the 'les' object pronoun.
I don't know if it's correct in terms of grammar, but it doesn't sound natural at all.
Since "(a) ellos" is the indirect object ("speak to them" and not "speak them"), you could say "les" + verb or "les" + verb + "a ellos", but we don't tend to say "a ellos" only.