I don't think the incentives (for VCs and founders) associated with cash and "services" investments are equally aligned. The main reason is not the potential for overbilling, which you mentioned, but because the VC gains a significant amount of influence over the company when the company hires the VC's close associates, which generates a conflict of interest.

But back to the billing: it is in the VC's best interest to acquire the largest possible percentage of the company at the lowest possible cost. When the VC is investing "services" instead of cash, and has control over the pricing of the services, it would be in the VC's interest to provide a smaller quantity of services in exchange for the same amount of equity, since this decreases the VC's cost of investment.

You're right that it would not make sense for the VC to make a deal that is egregious enough to choke the company's growth, since that would diminish the value of the equity, but rational VCs would not intentionally make such a deal. Also, since the services in this arrangement cost the company equity, not cash, I think overbilling would only hurt the company through opportunity costs (as the equity could have been used to obtain a better offer).

Whether it makes sense for the VC to overbill for services also depends on how much equity the VC owns. Most of my above comments operate under the assumption that the VC owns a small percentage of the company.