TPE can't be combined with a player, only with draft picks.
The TPE can't be combined with a player to cover the incoming salary, yes. However, if the TPE alone is large enough to cover the incoming player's salary, additional players can be included in the trade.
In essence, BOS would use the TPE to cover Asik's salary. Sending Olynyk would have no bearing on that. HOU would also be able to take on Olynyk because TPE are non-transferrable and don't actually count as incoming salary. However, HOU would receive a 'new' TPE of their own for the difference between Asik's contract and Olynyk's.